bluuebunny/crossref_metadata_2025 huggingface dataset:
Isothermal Permeabilities from Thermoosmosis Experiments
Authors: Bearman Mirion Y. , Bearman Richard J.
Published: February 2011

With the use of strain gauge pressure transducers, an improved constant volume apparatus has been constructed for measurement of isothermal permeabilities of gases from thermoosmosis experiments. Permeabilities are reproducible to about ±5% accuracy and compare favorably with those obtained by alternative techniques. Revised values are presented for permeability coefficients of the noble gases in rubber.
Behavior of Viscoelastic Materials in Short-Time Processes
Authors: Metzner A. B. , White J. L. , Denn M. M.
Published: February 2011

It is seen that great care is required in choosing constitutive equations which will correctly describe the behavior of viscoelastic fluids in processing equipment. The choices available, and their advantages and limitations, are considered through solution of a number of example problems. These considerations serve to develop scale-up criteria directly. The importance of the Deborah, Weissenberg, and Reynolds numbers in such problems is noted.
Molecular Weight Dependence of Relaxation Spectra of Amorphous Polymers in the Rubbery Region. VII. Comparisons of Experimental Relaxation Spectra with Those Estimated from Molecular Weight Distributions
Authors: Yasuda G. , Maekawa E. , Homma T. , Ninomiya K.
Published: February 2011

In a previous paper, the relationship between the relaxation spectrum of an amorphous high polymer in the rubbery region and the molecular weight distribution function was studied by the phenomenological theory method. We found a simple, direct proportional relationship between them. The reliability of assumptions and approximations made for the theoretical study can be evaluated by comparison of calculated and experimental data. As reported previously, selection of values for the simplified method was optional in calculating molecular weight dependence of the relaxation spectrum of a sample with a homogeneous distribution. Therefore, the feasibility of selection has to be evaluated by comparison of calculated results with observed data. For the comparison, it is necessary to obtain experimental data for a sample having a homogeneous distribution and compare it with calculated results for the relaxation spectrum and molecular weight distribution of the previous paper. However, these data are scarce in the current literature. From available past literature, we selected polystyrene, poly(vinyl acetate) and polyisobutene as typical samples of amorphous high polymers. In addition, experimental data for two samples of polystyrene were included. Thus, data for a total of five samples were compared with calculated results of the previous paper.
Anomalous Flow of Polyisobutylene
Authors: Lund J. Kenneth
Published: February 2011

This work began as a study of shear degradation in a polymer melt subjected to a uniform shear field. A new type of biconical rotor rheometer was designed and constructed for it. Early in the investigation, however, phenomena were observed which led our efforts away from the original objectives. Viscosity data on a polyisobutylene melt have been obtained which indicate the presence of two flow regions, having significantly different flow activation energies. Normal entanglement flow is encountered in one, the other is apparently dominated by a different mechanism, which results in lower flow activation energies. A mechanism involving rotating flow units is proposed and applied to describe this region.
Analysis of Flow of Shear Thinning Colloidal and Polymeric Systems Which Exhibit Elastic Recovery or Rigidity
Authors: Gillespie T.
Published: February 2011

The hydrodynamic-structural theory of viscosity is extended to take into account the possibility of a distribution of relaxation times. A new equation is presented which is easily applied to experimental data. The effect of a distribution of lifetimes is to extend the range of shear rate over which shear thinning occurs. When the ratio of the largest relaxation time to the smallest relaxation time is greater than 1 but less than 10 the new equation gives results in agreement with the Willamson equation. When this ratio of maximum relaxation time to minimum relaxation time is 300 ± 100 the new equation agrees with an equation recently suggested by Cross. The utility of the new equation is discussed and is illustrated by using it to determine the relaxation time spectra in polystyrene melts.
Structure of Polybutadienes
Authors: Bahary W. S. , Sapper D. I.
Published: February 2011

Polybutadienes made with six different catalyst systems were examined: (1) butyllithium, (2) “nickel-based”, (3) alfin, (4) “titanium-based”, (5) “cobalt-based”, and (6) free radical emulsion. The microstructure and macrostructure of the polybutadienes have been determined and are compared to the results published in the literature. These polybutadienes may be considered to be random terpolymers of cis, trans, and vinyl addition of butadiene. The glass transition temperature is specified by the vinyl content. The crystalline melting points of the high trans and also the high cis polybutadienes obey to a high measure Flory's equation for melting point depression of a random terpolymer. The molecular weights of the polybutadienes have been determined by light scattering and osmometry and the degree of long chain branching has been determined by the branching index, 〈g′〉. The macro-structural features of the linear polymers are confirmed by fractionation. However, the polydispersities calculated from fractionation data do not agree with those determined from light scattering and osmometry for the branched samples. The discrepancy is attributed to the method of characterization of the fractions. A distinction is made between molecular weight distribution and molecular size distribution.
Chemistry and Technology of Elastomeric Polysulfide Polymers
Authors: Bertozzi Eugene R.
Published: February 2011

The first synthetic rubber manufactured in the United States was of the polysulfide type. In 1927 Patrick and Mnookin had obtained the first of a series of patents on the products from the reaction of organic dihalides and inorganic polysulfides. Production was started in Kansas City in 1929 with the first of the polysulfide elastomers, the ethylene tetrasulfide polymer, under the trademark name Thiokol A. Thus, the Thiokol Chemical Corporation started its long association with the polysulfide polymers. Interest developed in many countries because of the potential cheapness and availability of the raw materials required. In the case of Thiokol A, these were sulfur, caustic soda, and ethylene dichloride from ethylene and chlorine. The most interesting property of these polymers was the unusual inertness to solvents and hydrocarbon fuels in contrast to the easy swelling of natural rubber. In this respect, Thiokol A was more inert than the polysulfide polymers to follow, but it had also some less desirable properties. It was difficult to process, had a bad odor that remained to some extent even when fully cured, and gave off irritating fumes during processing. It was subsequently found that the polymers from bis (2-chloroethyl) ether were free of this problem, processed better and gave improved physical properties. Thiokol B and Thiokol D were respectively the tetrasulfide and disulfide elastomers derived from bis-2-chloroethyl ether. These resulted from a study of the effect of polymer structure on polymer odor and properties that indicated a reduction in odor when the polysulfide units were separated by an increasing number of atoms. However, the process for making these polymers gave a high byproduct yield of the six atom heterocycle, thioxane, which has a pungent odor and no economic value. Five and six membered monosulfide rings are formed readily with the corresponding 1, 4- and 1, 5-dichloro aliphatic compounds.
Viscous and Elastic Behavior Attributed to Polymer Entanglements
Authors: Porter Roger S. , MacKnight William J. , Johnson Julian F.
Published: February 2011

Polymer chains are separated and behave as individual hydrodynamic units in sufficiently dilute solutions. A minimum polymer molecular weight, dependent on concentration, is necessary to produce the characteristic rheological effects generally attributed to entanglements. The minimum polymer molecular weights and concentrations for which entanglement effects are observed are called the characteristic entanglement compositions. Undiluted polymers exhibit such effects only above some minimum molecular weight. The common observation of entanglement effects indicates that they are not due solely to chemical or structural inhomogeneities. Polymer composition, e.g., polarity and perhaps tacticity, can lead, however, to changes in frequency and strength of entanglements. Entanglements appear to govern many important polymer characteristics, thus providing a strong motivation for their study. Characteristic chain spacings between entanglements have been reported from various viscoelastic experiments, low shear viscometry, nonNewtonian flow, and from relaxation times measured by nuclear magnetic resonance. The different techniques generally give concordant values, although with a wide variation in precision. For a few polymers, e.g., polydimethylsiloxane, the characteristic entanglement spacing has been calculated by each of the four techniques. For others, e.g., polyisobutylene and polystyrene, entanglement spacings have been reported by all except NMR. Entanglement effects have been treated theoretically by analogy with theories of rubber elasticity. Other theories have been developed based on breakage and reformation of entanglements and on polymer chain slippage. Certain of these theories have been shown to have the same formalism and yield similar conclusions. In general, the entanglement hypothesis provides a consistent interpretation for a variety of rheological data on concentrated systems of amorphous polymers, this despite the fact that an entanglement has not as yet been directly “seen”. A discussion of entanglements and the first method of calculating entanglement spacings was given by Mark and Tobolsky. A review in the field of polymer viscosities for concentrated systems has been recently prepared. Experimental details and theoretical derivations are given in texts. The notations used are defined in the Appendix.
Determination of Copolymer Molecular Weight
Authors: Rempp Paul , Benoit Henri
Published: February 2011

From this brief review it appears that determinations of molecular weight averages, of molecular weight distributions, and of compositional inhomogeneity of binary copolymers, require care in the choice of techniques and methods. Some of the most commonly used techniques for molecular weight determinations on homopolymers of various kinds are inadequate for the same determinations on copolymers. Others are more sensitive to fluctuations in composition than in molecular weights. Osmotic methods are the only one which are really insensitive to inhomogeneity, and which yield molecular weights. Ultracentrifugation in a density gradient yields precise information only on fluctuations in composition. Viscosity determinations require calibration, but even so, they may lead to erroneous values of the molecular weight in the case of copolymers. GPC is less sensitive to compositional heterogeneity, but cannot be applied for nonlinear copolymers. Finally, light scattering is a very powerful tool for studies on copolymers, since it leads to molecular weight averages and its helps characterize polydispersity and fluctuations in composition.
Application of High Resolution Nuclear Magnetic Resonance Spectroscopy to Elastomers in Solution
Authors: Chen Hung Yu
Published: February 2011

Use of high resolution nuclear magnetic resonance for polymer studies started late in 1950. The pioneer article of Bovey, Tiers, and Filipovich called attention to the potential of high resolution NMR for studies of polymer chain configurations. Since then, extensive use has been reported of high resolution NMR for various problems involving polymer structures. This review was originally intended to cover only studies dealing with rubber or elastomers. As the work proceeded, it became more obvious that the division of elastomers and non-elastomers appeared invisible so far as polymers in solution are concerned. Thus, it seems more appropriate to treat the subject in terms of polymers in general rather than limiting it only to elastomers. The review includes four main parts: namely, tacticity of polymer chain, orientation variation, or head-to-head or head-to-tail type variation of polymer chain, chain sequence distributions, and analytical measurements of structure and ratio of monomer units in polymer chains. This division is merely for convenience of discussion, but because of interrelationships existing in actual polymer systems, this partitioning will frequently appear not to be so precise. Excellent review articles on the subject appeared previously elsewhere; general articles are also available. Main object of this review is to furnish an up-to-date broad view of usefulness of high resolution NMR in polymer research. A more qualitative description, rather than a rigorous quantitative treatment is given each subject. Those who wish to pursue the subject in more detail should consult original articles. Extensive reviews on application of wideline NMR to polymer studies, which is not included in this review, are also available. Application of the recently developed spin-echo NMR technique to polymer solutions is not included.
Stress Strain Isotherms for Poly-(Dimethylsiloxane) Networks
Authors: Mark J. E. , Flory P. J.
Published: February 2011

Stress strain isotherms are presented for poly (dimethylsiloxane) networks of different degrees of crosslinking, swollen to various extents by a diluent. Results are interpreted in terms of the equation f*v21/3V/(α−α−2)=2C1+2C2α−1, where ƒ* is the tension per unit initial area (unswollen) exhibited by a network when swollen to a polymer volume fraction v2 and elongated to the relative length α, 2C1 is a parameter of the network structure established by the molecular theory of rubber elasticity, and 2C2 is an additional parameter found to give a better representation of experimental data. Values of C2 obtained for networks are found to decrease as the degree of crosslinking is decreased, and the degree of swelling is increased.
Dynamic Properties of Pbna-Natural Rubber Vulcanizates
Authors: Payne A. R.
Published: February 2011

Some crystalline organic compounds containing a β-naphthyl group stiffen rubbers considerably. This paper discusses the dynamic behavior of these systems when subjected to oscillatory strain of increasing amplitude. Modulus strain amplitude plots similar to that in carbon black-natural rubber systems are obtained. The implication of these results to reinforcement theory is discussed.
Investigation of Carbon Chains in Rubber Vulcanizates by Means of Dynamic Electrical Conductivity
Authors: Voet Andries , Cook F. Russell
Published: February 2011

Previously obtained dynamic shear modulus data over a wide amplitude range of rubber vulcanizates loaded with carbon blacks of widely varying structure as well as graphitized black were augmented with dynamic conductivity data at 30° C and at 100° C. Results confirm the existence of reversible transient and irreversible persistent carbon structures, the former being nearly completely destroyed at moderate shear amplitudes (50% strain), but effectively restored at lower amplitudes in a dynamic equilibrium between chain destruction and reformation. Higher structure blacks are characterized by a higher rate of chain rebuilding than lower structure blacks and by marked persistent chain alignment at higher amplitudes. Conductivity as a function of strain and time shows carbon chain behavior during stressing. The rates of destruction and rebuilding of the transient chains and the exact point at which the transient structure effects balance the chain alignment effects on conductivity have been established. The unusual behavior of vulcanizates loaded with graphitized black is explained.
Analysis of Contributions to Dynamic Mechanical Properties of Carbon Filled Vulcanizates
Authors: Voet Andries , Cook F. Russell
Published: February 2011

A method has been developed to separate quantitatively the contributions of filler volume, particle anisometry, and interaction with the elastomer to the dynamic modulus of carbon black loaded vulcanizates. The influence of reduction of transient structure by chemical promotion has been evaluated.
Lower Critical Solution Temperatures of Polybutadiene Solutions
Authors: Vanzo Ed
Published: February 2011

The lower critical solution temperature (LCST) is observed in polymer solvent systems as a rather high temperature above which the solution separates into two phases. This is a relatively recently discovered phenomenon, since it normally occurs above the boiling point of the solvent. Freeman and Rowlinson were apparently the first to report a LCST for hydrocarbon polymers in hydrocarbon solvents.
Role of Silicas and Silicates in Rubber Adhesion
Authors: Creasey J. R. , Russell D. B. , Wagner M. P.
Published: February 2011

The addition of resoreinol plus hexamethylenetetramine and/or hydrated silicas to rubber compounds can result in increased adhesion to textiles, wire, and other rubber compounds. Silica prevents loss of adhesion on aging or at elevated temperatures. The increase in adhesion is due, depending on the system, to improved wetting and hydrogen-bonding between the rubber compound and the substrate to which it adheres.
Fundamental Theory of Polymer Processing
Authors: Torner R. V. , Godkova L. S.
Published: February 2011

The theory of polymer processing is essentially a part of solid state mechanics. It basically consists of the theoretical and experimental investigation of motion and different physical-chemical processes in deformable viscoelastic systems. With this approach we could regard the great variety of known processing methods as a complex of separate problems the solution of each of which could be regarded as a particular example of the integration of a closed system of differential equations of motion under suitably specified initial and boundary conditions. This approach would enable us to examine in theoretical terms, and from a quite general viewpoint, the wide variety of phenomena which occur in processing machines including phase changes and chemical reactions.
Determination of State of Cure of Rubber-Cord Elements of Automobile Tires
Authors: Dozortsev M. S. , Sapronov V. A. , Reznikovskii M. M.
Published: February 2011

The possibility has benn demonstrated of using the Wallace microhardness gauge for determining the state of cure of rubber-cord elements of tires.
Application of Differential Thermal Analysis and Thermogravimetric Analysis to Elastomer Systems
Authors: Maurer J. J.
Published: February 2011

Judging by the increasing number of articles appearing in the literature, it appears safe to say that Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) are gaining acceptance and finding ever increasing use in the field of chemistry. The fact that this acceptance and increased interest is comparatively recent is really quite remarkable when one considers the comparative ease with which the techniques can be performed, and the many areas of applicability for them. This recent interest in two old techniques is probably related to two facts. First, the need for time-consuming construction of elaborate, precise equipment apparently previously presented too great an obstacle to all except the serious student or practitioner. Therefore, it was not possible for most workers to use routinely, or to investigate the utility of these thermal methods. This problem has been solved by the development and commercial availability of reliable, high-sensitivity equipment. Second, the polymer chemist has discovered the utility of these techniques and is beginning to exploit them. Because of the great size and scope of the field of polymer chemistry, this area may soon become the largest contributor to the thermal analysis literature. As one reviews the available literature on the application of DTA and TGA to polymers it becomes apparent that most of the articles, including reviews, are concerned with plastics—and that investigations of elastomers are actually few in number and relatively recent. One possible reason for this is that many of the plastics applications for DTA are concerned with the measurement of various aspects of crystallinity in polymers of high degree of crystallinity, especially polyolefins.
Radioisotope Methods of Analysis and Characterization of Elastomers
Authors: Campbell D. R. , Warner W. C.
Published: February 2011

Radioactivity applied to rubber technology encompasses such diverse areas as the effect of radiation on elastomers, use of strong gamma and beta sources for process control, and isotope methods to measure tire tread wear. These applications of radioisotopes have received considerable attention in recent years and the principles and techniques have been discussed extensively in both reviews and original papers. Significant contributions, however, have also been made in advancing elastomer technology through analytical use of radioisotopes of carbon, hydrogen, sulfur, and other beta-emitters, as well as by special radioisotope techniques. This survey discusses recent advances achieved with beta-emitters in vulcanization, diffusion, dispersion, adsorption, coagulation, and determination of functional groups in polymers. In addition, the value of activation analysis and other radioisotope investigative methods for characterization of elastomers is shown.
Course of the Terpolymerization of Ethylene, Proylene, and Dicyclopentadiene. I. Single Initial Addition of Dicyclopentadiene
Authors: Cunningham Robert E.
Published: February 2011

Detailed studies were made of the course of the terpolymerization of ethylene, propylene, and dicyclopentadiene to form unsaturated elastomers. All the dicyclopentadiene was added at the start of a polymerization, but the monoolefins were added continuously throughout the run. Under these conditions, unsaturation of the initial polymer is fairly high but decreases steadily as the reaction progresses. From analyses of the initial samples from each run, the catalyst of VCl4 (with A12Et3Cl3 cocatalyst), with heptane as the polymerization solvent, was most efficient for introducing unsaturation into terpolymer. This system also produces gel in the terpolymer in the latter stages of reaction, however. Catalysts of VCl4, VOCl2, or V(C5H7O2)3, with Al2Et3Cl3 cocatalyst, in benzene solvent gave terpolymers of quite similar unsaturations. With all systems, terpolymer yield increases very rapidly in the first few minutes of reaction, then very slowly for the remainder of the 30-min reaction time, reflecting the rapid loss of activity of the vanadium catalysts. Molecular weight growth of the terpolymer prepared in heptane was extremely rapid, reaching a high value in a few minutes. When prepared in benzene, the terpolymers showed a steady increase in molecular weight throughout the reaction but reached only a moderate final value (as expressed by inherent viscosity).
Configuration of Isoprene Structure in Butyl Rubber by Time-Averaging High Resolution Nuclear Magnetic Resonance
Authors: Chen Hung Yu , Field J. E.
Published: February 2011

In making butyl rubber, a small amount of isoprene is usually copolymerized with the isobutylene to facilitate vulcanization. The isoprene component thus incorporated in the butyl rubber can be present in three possible configurations, i.e., 1,4-, 1,2-, and 3,4-. The question concerning which of these configurations was the prevalent one in butyl rubber was investigated by Rehner in 1944. His chemical method was based on the fact that only butyl rubber with isoprene units in 1,2- or/and 3,4-configurations would yield formaldehyde and formic acid on ozonization. Since these compounds were not detected in this reaction product, he concluded, indirectly, that the isoprene segment in the butyl rubber was essentially in the 1,4-configuration. In this communication, we would like to report that, by means of a time-averaging high resolution nuclear magnetic resonance method, we are able to observe the absorption peak due to the 1,4-isoprene unit in a typical commercial grade butyl rubber. Since the IR has failed to detect such low concentrations of isoprene in the butyl rubber, the present NMR result seems to be the only direct observation of this structural component. We would also like to point out that such measurements may be useful in determining quantitatively the isoprene unit in butyl rubber as well as other polymers with minor constituents such as the third monomer unit in ethylene propylene terpolymer.
Extraction of Low Molecular Weight Materials from Gel Spherules, Using the System: Benzoic Acid/Cyclohexane/Crosslinked Polyisoprene
Authors: Hummel K. , Fuge Ch
Published: February 2011

Solid spherules of polyisoprene with different crosslink densities, radius 3 mm, were produced in closed, two-part steel molds, at 150° C, from purified natural rubber containing cumyl peroxide, (0.3 to 40 mmol/100 g of polymer). The spherules were swelled in a solution of benzoic acid (1.3 weight per cent) in cyclohexane at 25° C is equilibrium which was reached after about two days. Equlibrium swelling Q is defined as the weight ratio, swelling agent/polymer, for the polymer swelled to equilibrium; 1/Q increases with crosslinking and serves therefore as a measure of crosslinking. The swelled spherules were extracted with cyclohexane or water, at 25° C, in a flow-through, agitating vessel (with vigorous stirring of the liquid) in such a way that the concentration of benzoic acid in the extract was always negligibly low compared to the average concentration in the gel-phase. Quantity of benzoic acid in the gel spherule, M0, was determined before extraction, and also the residual quantity, Mt, as a function of extraction time.
The Migration of Extender Oil in Natural and Synthetic Rubber, III. Relative Contributions of Principal Structures in Aromatic Fractions to Diffusion
Authors: Lewis James E. , Deviney Marvin L. , Corman Blaine G.
Published: February 2011

Migration in rubber is a general phenomena of practical importance. A basic program using radiotracers was undertaken to help understand this migration and establish a rating system to allow the compounder to predict the behavior of a given oil from its molecular structure and that of the elastomer. The aromatic portion of a 14C labelled aromatic oil was separated into fractions of relatively narrow molecular-type distribution by silica gel solid—liquid chromatography. Static migration studies were made in natural rubber, SBR, cis-polybutadiene and emulsion polybutadiene rubber over the temperature range 50–125° C. Computer-derived diffusion coefficients were calculated, normalized by a least squares technique and used to calculate migration activation energies and to correlate the diffusivity of the oil fractions with degree of aromatic condensation. The data obtained indicate that moderate variations in the molecular composition of the aromatic components of an extender oil would have only a minor effect on the migration characteristics of the total oil.
Hydrogen Evolution from Natural Rubber During Tensile Tests
Authors: Andrews E. H. , Reed P. E.
Published: February 2011

Tensile tests performed on oriented natural rubber (NR) at temperatures below −120° C have produced an interesting phenomenon of foaming caused by the evolution of hydrogen. The unfilled natural rubber was oriented by extending it by 100% at room temperature and then cooling it to the test temperature of −120° C. At this temperature the amorphous material is in the glassy state and no crystalline material is present. It was expected that under these test conditions the rubber would fail in a brittle manner but at a slow extension rate of 0.2 cm/min a yield point was reached and the specimens then underwent extensions of up to 200% in excess of the initial 100%. After removal from the test chamber the specimens had a whitish appearance and as they warmed up considerable swelling took place (Figure 1) and large bubbles formed on the surface. Figure 2 shows a freshly cut surface through a foamed region. These surface bubbles often burst noisily. After several hours all signs of foaming had disappeared except for the craters left from burst bubbles and the material was again rubbery. The gas emitted from the foamed material was collected over water and, on analysis by GLC and mass spectrography, was found to be pure hydrogen. The evolution of hydrogen from NR has been previously reported during irradiation where according to one explanation it could be due to main chain breakage followed by the free radical joining another chain with the subsequent evolution of hydrogen. It therefore appears that at low temperatures and low strain rates, main chain rupture occurs during yield, the broken chain ends then attaching themselves to other chains. Such a process should increase the number of crosslinks in the material and hence reduce the intercrosslink molecular weight (Mc). Swelling tests on the material before and after foaming show that Mc is reduced from 6650 to 4900, basing the calculation on the Flory—Rehner equilibrium swelling equation.
Mechanical History Effects in the Crystallization of cis-1,4-Polybutadiene
Authors: Mitchell J. C.
Published: February 2011

Dilatometric studies have revealed alterations in the crystallization kinetics of cis-l,4-polybutadiene subjected to the shearing action of a laboratory mill. Reduction in the Avrami exponent by more than one unit suggests that, in addition to a change from pseudo-homogeneous to instantaneous nucleation, a change in the growth mechanism of the new phase is involved. These changes are presumed to be brought about either by sub-optical microscopic ordering of the amorphous polymer (e.g., the ‘quasi-indestructible’ clusters proposed by Rabesiaka and Kovacs) or by shear effects on. impurity constituents, with either effect leading to row orientation.
Recrystallization and Melting of Partially Melted Stark Rubber
Authors: Roberts Donald E.
Published: February 2011

Two specimens from a piece of stark rubber which had a melting temperature originally at 41° C were partially melted at 38° C and allowed to stand for 11 years, one at about 25° C, the other at 38° C. The first showed a continuous slow decrease in specific volume, while the second increased slowly in volume for 5 months and remained constant for about 5 months more before showing the continuous slow decrease. The melting temperature of the first increased to 45° C and the melting range was broadened. The melting temperature of the second became 52° C and the range was narrowed. Perfecting or enlarging of crystals and the effect of higher recrystallization temperatures have influenced the melting temperatures. The effect of heating rate is discussed in connection with slow increases in volume, attributed to relaxation of oriented regions, during melting.
Poisson's Ratio for Stretched Vulcanized Natural Rubber
Authors: Sekiguchi H. , Kakiuchi M. , Morimoto T. , Fujimoto K. , Yoshimura N.
Published: February 2011

Changes in the Poisson's ratio of natural vulcanized rubber due to elongation were investigated experimentally. The following results were obtained: If infinitesimal deformation at any instant during elongation is considered, it appears to be correct to take the Poisson's ratio at such instants as 0.5. If the apparent Poisson ratio when a certain standard mark is taken and a large deformation imparted is considered, and the elongation ratio is made α, the Poisson's ratio decreases from 0.5 in accordance with the equation log10 (1/m)=0.0204α2−0.261α−0.0628. This equation is valid for subsequent elongations, no matter what elongation situation is taken for the standard marks. These two results do not vary with the carbon black content or on repeated stretching.
Behavior of Unfilled and Filled Rubbers in Shear in the Glass Transition Region
Authors: Schwarzl F. R. , Bree H. W. , Nederveen C. J. , Schwippert G. A. , Struik L. C. E. , Van der Wal C. W.
Published: February 2011

Rubbers filled with high amounts of a hard inorganic filler still show typical mechanical properties of a high polymer, viz., a glass transition region, a glassy state and a rubbery state. Effects of filler characteristics on the glass transition are discussed, chiefly on the basis of the course of shear modulus at constant frequency as a function of temperature. Effect of volume content of filler on the glass transition of composite materials consists chiefly in a change of the levels of shear modulus in the glassy and in the rubbery state. This change may be described by a simple macroscopic model due to van der Poel. Predictions by this theory could be confirmed for rubbers filled with single filler fractions in the filler size range 30 to 500 µm, and in the range of filler content 0 to 50 vol%. At smaller particle sizes, an effect of filler size was observed, which points to increase in the transition temperature and to increase in the level of modulus in the rubbery state with decreasing filler size. Preparation of composite materials with high filler contents (>55 vol%) is only possible by using a filler with a bimodal size distribution. In this case, moduli depend on filler content and mixing ratio of coarse to fine filler fraction; the van der Poel theory then gives predictions which are too high in comparison with experimental results.
Influence of Carbon Black Structure on Vulcanizate Properties
Authors: Price C. R. , Aboytes Peter
Published: February 2011

Samples of carbon black representing regular and high structure levels of HAF and ISAF were subjected to ball milling under an inert atmosphere for varying periods of time. The structure level varied inversely with duration of ball milling. Tests of the various blacks in SBR revealed that the persistent or reinforcing structure was changed by ball milling and not just the transient structure. It was also shown that laboratory abrasion resistance was greatly reduced by reducing the structure below a level of DBP absorption of 100–110 cm3/100 gms. Above this level, structure did not seem to contribute significantly to abrasion resistance.
The Measurement of Cord Tensions in Tires
Authors: Patterson Ralph G.
Published: February 2011

Tensions were measured in the reinforcing cords of tires during curing, post-inflation, and in service, using a miniature transducer employing resistance strain gauges. Cord tension varied throughout the cure cycle and was influenced by temperature, ply fabric width, cord modulus, and shrinkage. The cord tension reached a maximum (i.e., 2.2 lb) immediately after mold closing when the tire was forced out to mold dimensions. The tension was proportional to the fiber modulus and inversely proportional to the width of ply fabric. About two minutes after mold closing, the tension decreased sharply because the rubber became soft. The cord position shifted in the rubber and the tension was removed. Thereafter, thermal shrinkage of the fiber determined the cord tension as the tire temperature increased and the rubber cured around the cord. During post-inflation, tension was proportional to inflation pressure and reached 5.0 lb at 35 psi. Under these conditions, the cord stretched and tire size was related to cord extensibility. Tension in the cured tire increased in proportion to inflation pressure and was at a maximum at the tread center (3.0 lb at 24 psi), decreasing toward the bead to 2.3 psi. These findings were in agreement with calculations based on membrane theory. In straight running, cord tension in ply one opposite the center of the tread followed an essentially sawtooth pattern, decreasing below the inflation tension (from 3.0 lb to 1.4 lb) and returning to the inflation tension as the point of measurement moved into and out of the deflected region at the road surface. Increasing or decreasing inflation pressure shifted the sawtooth profile up or down without changing its basic shape. At constant pressure (i.e., 22 psi), increasing load from 700 to 1200 pounds increased the tension decrement from 1.1 to 1.5 lb. The principal effect of speed was to increase the overall tension because of higher operating pressure without significantly changing the sawtooth pattern. A condition of severe overloading, underinflation, or a combination of the two caused the cord in the sidewall to go into compression. This is believed to contribute to fatigue damage, based on previous work.
Evidence for Chemical Interaction in Carbon and Polymer Associations. Extension of Original Work on Effect of Carbon Black Structure
Authors: Gessler A. M.
Published: February 2011

Selected proposals regarding the mechanism of carbon and polymer interaction were reviewed from the literature. With this material as background, the bound rubber capacity of low and high structure HAF blacks was studied over a broad concentration range in four previously unstudied polymers: ethylene-propylene copolymer, chlorinated butyl, cis-1,4-polybutadiene, and natural rubber. Experimental evidence from the resulting work was combined with that from a similar previous study involving five polymers: polyisobutylene, butyl, two ethylene-propylene terpolymers differing in free radical activity, and SBR. With low structure black, the extent of bound rubber formation varies with the activity of the polymer functionality, in accordance with expectation. Previously proposed mechanisms for the bonding of rubber and black are used to resolve the differences which are shown. With high structure black, the primary carbon-to-polymer bonding effects referred to above are overshadowed by the formation, in situ, of a facile, new free radical source which is proposed to result from the mechanical breakage of aggregated carbon black structure during the milling of rubber and black. This imposed free radical activity is shown to have a profound effect on the subsequent behavior of the polymer. The inclusion of sulfur (2.0 php) in bound rubber systems leads to some extremely interesting results. Except for natural rubber, polymer is not crosslinked by the action of sulfur alone, even when the systems are heated as in vulcanization. The high bound rubber levels which are formed when sulfur and black are both present, especially with butyl, are proposed to result first from a reaction of sulfur with the black, and second, from reaction of this sulfur-modified black with the polymer. The close relationship between vulcanization and reinforcement is thus attested.
Electrical Properties of Stretched Carbon Black Loaded Vulcanizates
Authors: Voet Andries , Sircar Anil K. , Mullens Troy J.
Published: February 2011

To study the function of the carbon network, electrical conductivities and dielectric constants were measured on carbon black filled vulcanizates through the full range of elongation. Data were obtained for a variety of elastomers and carbon blacks, at different loading levels and covering the commercial particle size and structure ranges. The influence of the temperature and strain rate was investigated. In most of the reinforcing blacks there is a pronounced fall in conductivity and a minor decrease in dielectric constant in the first area of elongation, corresponding to the elimination of the transient structure. This is followed by an area of steady increase, caused by alignment of persistent carbon chains. At still higher elongations a sharp decrease occurs, due to destruction of carbon-elastomer bonds. The first two effects are very pronounced in high structure blacks but negligible in very low structure reinforcing blacks. The third effect leads to hysteresis and irreversible changes in the vulcanizates. Graphitized carbon black, with little or no bonding to the elastomer, does not show the third effect. Particle-elastomer adhesion data, obtained by an electron micrographic replica technique, independently confirmed the results. Anisotropy in electrical conductivity was observed. The major significance of the carbon filler in stress softening is discussed.
Migration of Antioxidants and Accelerators in Natural and Synthetic Rubber II. Sulfenamide System Studies and Comparison of Age Resister Migration under Inert and Practical Conditions
Authors: Lewis James E. , Deviney Marvin L. , Whittington Lawrence E.
Published: February 2011

Radiochemical techniques developed for studying extender oil migration in various elastomers have been adapted for use in investigating the migration of age resisters and curatives. This paper contains basic diffusion coefficient data for nine compounds including both staining and nonstaining antioxidants and members of the sulfenamide, thiazole and thiuram accelerator series. Techniques for synthesizing these age resisters and curatives in the carbon-14 and sulfur-35 labelled form are described. Migration was studied in natural rubber, SBR, cis-polybutadiene and EPT vulcanizates. Computer techniques were used to calculate diffusion coefficients from radiochemical count data. Results from preliminary migration studies under practical curing and end-use conditions are also presented. In the case of phenyl-2-naphthylamine migration in cis-polybutadiene, a pronounced decrease in diffusivity with increasing surface area of the carbon black filler was observed.
Tel-Tak: A Mechanical Method for Estimating Both Tackiness and Stickiness of Rubber Compounds
Authors: Beatty J. R.
Published: February 2011

A simple method for measuring quantitatively tack and stickiness of rubber compounds has been developed. It may also be used to measure adhesion of tapes, adhesives etc. successfully. Results are in agreement with subjective evaluation of these properties.
Determination of Carbon-Bound Lithium in Polymer Cements
Authors: Turner R. R. , Gaeta L. J. , Altenau A. G. , Koch R. W.
Published: February 2011

A simple and direct titration procedure for the determination of carbon-bound lithium in lithium catalyzed polymer cements has been developed. It utilizes the specific reaction of allyl bromide with carbon-bound lithium. Since this procedure was used for a solution of polymer in hydrocarbon, reagents were selected to avoid phase separation. This procedure has been used over a catalyst range of 1.5 to 0.5 millimoles per hundred weight polymer. The resulting polymers had molecular weights from fifty thousand to five hundred thousand.
Ozone Crack Initiation: Statistical and Deterministic Interpretations of Action of p-Phenylenediamines and EPDM as Antiozonants
Authors: Ambelang J. C. , Wilson F. H. , Porter L. E. , Turk D. L.
Published: February 2011

The time to first visible crack of ozone sensitive vulcanizates appeared to be short and replicable 3–5 h at 25 pphm ozone, 2 h at 50 pphm. For antiozonant protected OE-SBR below the critical strain, the time to first visible crack was found to be a stochastic value with a normal or log normal distribution.
Carbon Black Morphology: I. Particle Microstructure. II. Automated EM Analysis of Aggregate Size and Shape
Authors: Hess W. M. , Ban L. L. , McDonald G. C.
Published: February 2011

Carbon black particle and aggregate microstructure were studied in detail by means of high resolution electron microscopy. Improved instrumental and environmental conditions have enabled more detailed studies on the size, orientation, and spacing of graphite layers in carbon black particles than heretofore possible. The layers form continuous networks about particle growth centers and between adjoining particles and show a paracrystalline orientation rather than individual crystallites. Based on this type of orientation carbon black primary aggregates are now defined as single graphite paracrystals exhibiting either a fibrous (furnace and channel blacks) or spheroidal (thermal blacks) shape.
All-cis Polypentenamer: A Potential New Elastomer for Low-Temperature Applications
Authors: Dall'Asta G. , Scaglione P.
Published: February 2011

On the basis of the above results it can be concluded that the low-temperature characteristics of all-cis polypentenamer are better than those of any other hydrocarbon elastomer and that they can even be competitive with those of much more expensive extremely low-temperature elastomers, like silicone rubber.
Dependence of the Crosslinking Efficiency on the Reaction Conditions in the Peroxide Crosslinking of Unsaturated Polyolefins
Authors: Aahikari Nobuyuki , Kawashima Izumi , Kawashima Takehisa
Published: February 2011

The crosslinking reactions of several unsaturated polyolefins with organic peroxides were carried out in an attempt to establish the dependence of the crosslinking efficiency on the reaction conditions, especially the reaction temperature and the peroxide concentration. Usually, the efficiency gradually increased up to a certain temperature and then decreased abruptly. This efficiency decrease can be considered to be due to (1) a decrease in the hydrogen abstraction, which is one reaction producing crosslinks, and (2) an increase in the termination rate in a chain reaction arising from opening up the double bond, which is another reaction producing crosslinks. Except for cases in which an extremely high temperature was employed or when a very high concentration of peroxide was used, the efficiency decrease by scission at higher temperatures seems to be comparatively small.
Viscoelastic and Ultimate Tensile Properties of Styrene-Butadiene-Styrene Block Copolymers
Authors: Smith T. L. , Dickie R. A.
Published: February 2011

A study was made of the stress—strain and ultimate properties in simple tension of an elastomeric styrene—butadiene—styrene block copolymer (Kraton 101) and also of a similar material (Thermolastic 226) that contains about 35% plasticizer as well as inorganic pigments. Stress—strain data were obtained at crosshead speeds from 0.02 to 20 in./min at temperatures from − 40 to 60° C. The relaxation rate, derived from the data at constant extension rates, was about 8% per decade of time for both materials at temperatures from − 40 to about 40° C and at extensions from about 20% up to 400%. Above − 30° C, the shift factor log aT was found to vary linearly with temperature. These findings indicate that the time and temperature dependence of the mechanical properties results primarily from the plastic (or viscoelastic) characteristics of the styrene domains. The tensile strength for Kraton 101 below 40° C is somewhat greater than 4000 psi, sensibly independent of extension rate and temperature. For the highly plasticized Thermolastic 226, the tensile strength at an extension rate of 1.0 min−1 increases from 2200 psi at 0° C to 3600 psi at − 40° C. Above 40° C for Kraton 101 and above 0° C for Thermolastic 226, the tensile strengths are dependent on extension rate and temperature owing to the increased ductility of the styrene domains. The high strength of these materials results from the uniformly dispersed styrene domains of colloidal dimensions. To obtain a crack of sufficient size to satisfy an energetic criterion for self-sustained high-speed propagation, domains must be disrupted. The plastic characteristics of the domains have a controlling effect on crack growth and thus on the ultimate properties of the materials. The strength and extensibility of other elastomers are considered in relation to those of the block copolymers.