bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture of Amorphous Polymeric Solids: Reinforcement
Authors: Halpin J. C. , Bueche F. 
Published: February 2011

Abstract
Although the tensile stress at break (σb) and the corresponding ultimate elongation (αb) of a reinforced elastomer depend markedly on temperature and test rate, characteristic time-to-break curves can be obtained utilizing the Leaderman-Tobolsky-Ferry superpositioning techniques. In addition, a distinctive failure envelope is obtained when the logσbT0/T is plotted against log(αb−1), where T and T0 (° K) are the test temperature and an arbitrary reference temperature. Delayed rupture experiments yield qualitatively the same results as forced rupture experiments. Furthermore, an analysis of the Leaderman-Tobolsky-Ferry shift parameters indicate a concomitant increase in the apparent activation energy with increasing reinforcement concentration. These observations are explicable by utilizing the failure theory of Bueche and Halpin. It is now apparent that failure is the result of the propagation of tears or cracks within the viscoelastic body and that the time and temperature dependence of the ultimate properties is directly related to the time-temperature dependence of the modulus. A preliminary picture of the salient molecular events is presented.
Cut Growth and Fatigue of Rubbers. I. The Relationship between Cut Growth and Fatigue
Authors: Gent A. N. , Lindley P. B. , Thomas A. G. 
Published: February 2011

Abstract
The relationship between the cut growth and fatigue failure of natural rubber vulcanizates under repeated loading is examined. The cut growth behavior has been investigated using several types of test piece, and the results are shown to be consistent when interpreted in terms of the tearing energy concept developed previously. The most comprehensive data have been obtained by measuring the growth of a small cut in the edge of a strip cycled in simple extension. It is found that the cut growth per cycle is approximately proportional to the square of the maximum tearing energy attained during the cycle. Using this relation, the fatigue life of a specimen containing a small cut is deduced from elasticity theory as a function of initial cut size and maximum strain. Experimental results give good agreement with theory. A similar strain dependence is found for the fatigue life of die-stamped dumbbell test pieces with no intentionally produced flaws; this is consistent with the mechanism of failure being cut growth from small flaws present in the specimens. Their effective size is estimated to be about 2×10−3 cm, which is compatible with the observed superficial imperfections of the cut edges.
Cut Growth and Fatigue of Rubbers. II. Experiments on A Noncrystallizing Rubber
Authors: Lake G. J. , Lindley P. B. 
Published: February 2011

Abstract
Tensile fatigue failure of a gum vulcanizate of noncrystallizing SBR can be accounted for by the growth of small flaws initially present in the rubber. Fatigue of crystallizing natural rubber was shown in Part I to be attributable to the same cause. Cut growth results are interpreted in terms of the tearing energy theory of Rivlin and Thomas. SBR exhibits cut growth under both static and dynamic conditions; in each case the rate is approximately proportional to the fourth power of the tearing energy. Variation of the dynamic cut growth rate with frequency can be explained by the summation of a time-dependent static component of growth and a cyclic component not dissimilar to that occurring in natural rubber. Fatigue failure, under both static and dynamic conditions, is predicted from the cut growth results. These predictions are found to account quantitatively for experimentally observed fatigue lives when a suitable value is assumed for the initial flaw size. Fatigue lives at different temperatures correlate well with cut growth results obtained by Greensmith and Thomas over the same temperature range. The results are compared to those obtained previously for natural rubber, and possible reasons for the differences in fatigue behavior of crystallizing and non-crystallizing rubbers are discussed.
Studies in the Thermodynamics of Polymer-Liquid Systems. I. Natural Rubber and Polar Liquids
Authors: Booth C. , Gee G. , Holden G. , Williamson G. R. 
Published: February 2011

Abstract
There is a great lack of reliable thermodynamic data on concentrated polymer solutions. This group of papers contributes further measurements, especially on systems consisting of a polar liquid and nonpolar polymer, and presents a review of the current situation. This first part records observations on the swelling of natural rubber in several polar liquids, using two different techniques. One of these is the conventional study of vapor pressures; the other is a novel procedure involving measurements of swelling and tension in stretched crosslinked samples. The results are compared with the Flory-Huggins equation, and show that as swelling proceeds and approaches saturation, there is a marked fall in the interaction parameter χ`. At the same time the entropy of dilution falls progressively further below the curves predicted by current theories.
Studies in the Thermodynamics of Polymer-Liquid Systems. II. A Reassessment of Published Data
Authors: Booth C. , Gee G. , Jones M. N. , Taylor W. D. 
Published: February 2011

Abstract
Part II contains a complete reassessment of all published data on polymer solutions, using a single method of analysis. Non-polar liquids in non-polar polymers show an entropy of mixing higher than predicted by current theories. The discrepancy is attributed to a degree of order in the solid polymer. Polar liquids in non-polar polymers follow the pattern described in Part I: this behavior is attributed to non-random mixing at concentrations approaching saturation.
Contribution to the Study of Ethylene-Propylene Copolymers by Infrared Spectroscopy. Distribution of Monomeric Units
Authors: Bucci Giovanni , Simonazzi Tonino 
Published: February 2011

Abstract
Elastomeric properties of ethylene-propylene copolymers depend not only on the composition but also on the copolymer microstructure, i.e., on the distribution of monomeric units along the macromolecular chain. According to Natta and coworkers the best polymer should be obtained when two monomeric units are randomly alternated in the macromolecule. The random alternation of the monomers is actually only partial because somewhat longer homosequences are formed. In such a case one deals with block polymers. On the basis of some theoretical considerations on the copolymerization process and also on the basis on the reactivity ratios of the two monomers, Natta and coworkers have calculated the distribution functions of sequences for various catalyst systems. Infrared spectroscopy has been widely used in connection with this problem though from different viewpoints and with different aims. The purpose of our work is to reanalyze the whole problem. We have focused our attention on the CH2 rocking band in the sequence (—CH2—)n, where n varies from 1 to 5 or more. Some disagreement exists between various authors on the assignment of these bands, especially in the case of the (—CH2—)3 and (—CH2—)4 sequences. We have then divided our work as follows: (a) assignment of infrared bands in the spectral region between 900 and 650 cm−1; (b) calculation of absorbances at various frequencies; (c) attempt at a numerical evaluation of the distribution of monomeric units.
Use of Sol-Gel Analysis to Estimate Chain Scission during Vulcanization. II. Peroxide Vulcanization of Synthetic cis-Polyisoprene
Authors: Bristow G. M. 
Published: February 2011

Abstract
Sol-gel analysis indicates that in the vulcanization of synthetic cis-polyisoprene by cumyl peroxide there are only 2–3 sites of scission per 100 crosslinked isoprene units, a value closely comparable with that observed for natural rubber.
Bonding of Fibrous Glass to Elastomers
Authors: Vanderbilt Byron M. , Clayton Robert E. 
Published: February 2011

Abstract
Elastomers can be bonded to fibrous glass using a chemical at the interface which is capable of reacting with both glass and rubber. Organic silanes have proven most useful for this purpose. Unsaturated silanes are very effective for bonding glass to peroxide-cured elastomers. Use of a nonconjugated diolefin as coupling agent between silane and elastomer greatly enhances the degree of bonding. Certain substituted alkyl silanes are effective when used with the right combination of rubber and curative. Bonding strengths at ordinary temperatures approach or exceed those of the respective vulcanizates. Glass-elastomer adhesions at elevated temperatures show promise. All commercial elastomers can be effectively bonded to fibrous glass.
Elastic Stability of Rubber Compression Springs
Authors: Gent A. N. 
Published: February 2011

Abstract
Experimental measurements are described of the critical (buckling) compressive loads for columns of rubber springs under various loading conditions. They are shown to be in good accord with the theoretical treatment of Haringx, in which the classical theory of buckling is modified to take into account the shear deflection of column elements. Measurements are also described of the shape of the buckled column and of the shear stiffness of columns under compressive loads smaller than the buckling load. They are found to be satisfactorily described by the theory also.
Elastomeric Polycarbonate Block Copolymers
Authors: Goldberg Eugene P. 
Published: February 2011

Abstract
Polycarbonate block copolymers were prepared by phosgenating pyridine solutions of polyether glycol-bisphenol-A mixtures. Copolycarbonates derived from poly(oxyethylene) glycols (Carbowaxes) were studied in detail for property-structure effects as a function of glycol molecular weight (1000–20,000) and copolymer composition (5–70 weight per cent or 0.3–10.0 mole per cent of a 4000 molecular weight glycol). Remarkable strength (&gt;7000 psi) and snappy elasticity (&gt;90 per cent immediate recovery) were observed at poly(oxyethylene) block concentrations greater than 3 mole per cent. These thermoplastic elastomers also exhibited high softening temperatures (&gt;180° C) and tensile elongations up to about 700 per cent. Both Tg and softening temperature varied linearly with comonomer mole ratio over the composition range studied, with Tg displaying much greater polyether concentration sensitivity. It is suggested that the observed property effects result to a large extent from the variation in poly(bisphenol-A carbonate) block length that accompanies the changing of copolymer composition. An initial increase in flexural modulus (stiffness) was observed at low polyether concentrations (0–1 mole per cent). This phenomenon is considered to be related to similar modulus effects found in plasticized rigid thermoplastics at low plasticizer concentrations. A moderate degree of molecular order, due to bisphenol carbonate segments rather than the normally crystalline polyether, was detected by x-ray analysis. Elastomeric carbonate-carboxylate tetrapolymers were also prepared by partial replacement of carbonate with isophthalate, terephthalate or adipate linkages in polyether-bisphenol systems. The dramatic softening temperature depression observed in this class of polymers is attributed to the disruption of long bisphenol carbonate block sequences that exist in the simpler polyether glycol-bisphenol carbonate copolymers.
Reactions between Peroxide and Polydiolefins
Authors: van der Hoff B. M. E. 
Published: February 2011

Abstract
Reactions of cumyl peroxide with polyisoprenes and polybutadienes are compared. Hydrogen abstraction from polyisoprenes and recombination of polymer radicals yield a network with crosslink concentration equal to that of decomposed peroxide. The concentration of crosslinks in polybutadiene networks is much greater than that of decomposed peroxide. Values of the ratio of these two concentrations as high as 50 have been calculated from swelling measurements of the vulcanizates. The polybutadienyl radical attacks double bonds in the polymer; thus crosslinks are formed by propagation. Infrared analysis shows that propagation proceeds via unsaturation in the main chain as well as via double bonds of vinyl side groups. The experimental relation between crosslink concentration and antioxidant concentration is consistent with a reaction scheme based on termination of polymer radicals by antioxidant only.
Anionic Polymerization of Isoprene
Authors: Worsfold D. J. , Bywater S. 
Published: February 2011

Abstract
Polymerization of isoprene with butyllithium in cyclohexane has been studied. The initiation reaction was found to be complex; plots of conversion of butyllithium against time are sigmoidal. The order with respect to the initiator was found to be between one-half and one. The order of the isolated propagation reaction in polyisoprenyllithium was found to be one-quarter and was correlated with a fourfold association of active chain ends determined by dilute solution light-scattering measurements. The major effect of tetrahydrofuran on the reaction was the great increase of the initiation rate. The kinetic order changes slowly with the addition of small amounts of tetrahydrofuran, suggesting that the aggregates are broken down with difficulty. The microstructure of the polymer has been determined by NMR measurements and shows a steady transition from a largely 1:4 to a largely 3:4 structure as the polarity of the solvent is increased by the addition of tetrahydrofuran.
Mechanochemical Effects in Fatigue of Rubber
Authors: Reztsova E. V. , Chubarova G. V. , Slonimskii G. L. 
Published: February 2011

Abstract
1. It has been shown that the effectiveness of the action of antifatigue agents changes depending on the method of addition to the rubber. 2. The change in effectiveness of such agents points to the fact that there is significant connection between mechanochemical phenomena occurring during milling and fatigue of the polymer, which must be taken into account in manufacturing practice. 3. The effect of preliminary milling of the rubber with antifatigue agents on fatigue life of the compound apparently can be explained as resulting from consumption of antifatigue agents in the milling process, owing to mechanochemical reactions.
Thermal Degradation of Ethylene Propylene Rubber. C2-C6 Hydrocarbons as Thermal Decomposition Products of SKEP
Authors: Slobodin Ya M. , Mayorova V. E. , Smirnova A. M. 
Published: February 2011

Abstract
1. Degradation of SKEP was carried out. 2. The qualitative and quantitative compositions of C2-C6 hydrocarbons in the products of degradation were established by gas-liquid chromatography.
A New Tear Test for Rubber
Authors: Veith A. G. 
Published: February 2011

Abstract
Knowledge of rupture properties is required to characterize rubbers in laboratory evaluation adequately and to attempt to estimate service performance. The most commonly measured rupture property is tensile strength. Tear strength, although known to be important, is measured less often due to a general consensus that existing tests are inadequate. This paper describes a new, practical, tear test method based on theoretical work by workers at the Natural Rubber Producers' Research Association (NRPRA). Their work has shown that a characteristic tear strength may be measured independent of testpiece geometry. A testpiece has been devised that circumvents two deficiencies inherent in the “trousers” testpiece advocated by NRPRA. These are: appreciable leg extension, and failure of the tear to propagate down the central axis when tear tests are carried out on a wide variety of vulcanizates. These deficiencies are overcome by reinforcing the legs with fabric and by molding a longitudinal groove of a definite cross-sectional geometry into the testpiece. These alterations of the basic trousers test specimen allow almost any type of rubber to be tested successfully. Detailed descriptions of the testpiece, mold, method of test, and tear curve analysis are given, as well as results of a statistically planned evaluation program. Effects of crosslink density, carbon black content, processing oil content, and test temperature are determined for natural rubber and SBR. The influence of speed of testing in a rather restricted range is also included. When modified trousers tear strengths are compared with tear strengths from a common test, ASTM D-624, Die C, pronounced differences are apparent. These are pointed out and deficiencies in the Die C test discussed.
New Approach to Tire Durability Testing
Authors: Coddington D. M. , Marsh W. D. , Hodges H. C. 
Published: February 2011

Abstract
A new fundamental approach to tire durability testing is described based on dynamic temperature build-up. This has been made possible by development of a practical technique for continuously measuring the internal shoulder temperature of tires during actual road operation at speeds up to 80 mph. Utility of this technique has been demonstrated in a systematic characterization of effects of load, inflation, speed, and ambient temperature on tire running temperature for tires made from two widely different elastomers, SBR and butyl. Within the scope of the experimental study, correlation of tire durability to running temperature has been developed. The dynamic temperature measuring technique and the apparent relations between running temperature and durability should have broad application in the tire industry.
Determination of Molecular Weight Distributions of Elastomers with the Ultracentrifuge
Authors: Henderson J. F. , Hulme J. M. , Small R. M. B. , Williams H. L. 
Published: February 2011

Abstract
The ultracentrifuge has been used to obtain molecular weight distributions of cis-1,4-polybutadiene and styrene/butadiene rubber. When corrections are made for the effects of centrifugal pressure and solution concentration, distributions are obtained that are in good agreement with those determined by elution chromatography. Rapid comparisons of polymers are sometimes possible, especially if the polymers are chemically similar.
Molecular Weight Distributions of Elastomers—Comparison of Gel Permeation Chromatography with Other Techniques
Authors: Gamble Leon W. , Westerman Lowell , Knipp Ebnest A. 
Published: February 2011

Abstract
During the past decade interest in polymer fractionation for evaluating molecular weight distribution has increased. New polymers, such as polypropylene, high density polyethylene and many others have been subjected to extensive characterization, but some older polymers, including natural rubber have not. In recent years column fractionation has received a great deal of attention; a review has been made by Schneider. Most of the techniques of polymer fractionation, such as precipitation from solution and column fractionation, are quite lengthy and require days or even weeks to complete. A more rapid method for molecular weight distribution has been the goal of polymer chemists for years. The most promising of the rapid methods are turbidimetric and gel permeation chromatography by which analysis is accomplished in a few hours. This paper discusses application of gel permeation chromatography to fractionation of elastomers. In addition this technique is compared with data from column fractionation, light scattering and osmometry. Some of the assumed factors used in converting gel permeation data into molecular weights are in error. But by calibration of the gel permeation chromatograph with classical methods reliable data can be obtained.
Fatigue Failure in Nylon Reinforced Tires
Authors: Patterson Ralph G. , Anderson Robert K. 
Published: February 2011

Abstract
The principal mechanism leading to fatigue failure of nylon cord tires is progressive loss of cord strength from filament ruptures that occur at an angle of approximately 25 degrees to the fiber axis. Flexing causes cords to become weaker until residual strength is less than tensile forces in the tire, at which time the remaining filaments break with a blunt-ended tensile rupture. Individual cords in tires have stress environments determined by such factors as cord spacing, uniformity, and stiffness of the immediate flexing region, which appear to influence significantly their fatiguing rate. It is probable that these factors also operate in laboratory in-rubber fatigue tests, so that a high degree of precision in sample preparation and loading conditions is essential for such tests to give reproducible data. Measurement of cord strength loss was found to be a valid and useful means for following the progress of fatigue when it was recognized that cords under opposite sidewalls of tires lost strength at markedly different rates, which were not linearly proportional to test mileage. The direction of tire rotation and the cord angle in a given ply determined which half of the ply lost strength fastest. Strength loss was higher for the half of the cord that led into the load bearing region of the tire as it rotated. This presumably happened because of unsymmetrical stress conditions, but no measurement of cord stress was made. Fatigue failures of tires generally occurred at localized points and resulted from failure of a few cords that lost strength faster than the surrounding cords. The failures occurred in the innermost ply at “hinge points” opposite the end of the flipper fabric in the ply splice.
Microstructures of Polydienes Prepared from Alkyllithium
Authors: Hsieh Heney L. 
Published: February 2011

Abstract
The stereochemistry of polymerization of isoprene and butadiene by means of alkyllithium initiators was examined. The stereochemistry of polybutadiene and polyisoprene responded to the same variables in anionic polymerization. Micro-structure of both polymers is sensitive to initiator level, solvent type, and polymerization temperature, but is independent of monomer concentration, conversion and initiator structure. The heat activation energy of the reaction leading to 1,2 addition is greater than of that leading to trans-1,4 addition (1200 cal/mole). The exact sequence leading to stereospecific polymerization of dienes by means of alkyllithium is still not clear. However, it seems to involve orientation of the incoming monomer units by association and passage through a transition complex in which all bonds are largely covalent in character and within which polymerization occurs.
Melting Point of cis-1,4-Polybutadiene
Authors: Mitchell J. C. 
Published: February 2011

Abstract
Melting point values for cis-1, 4-polybutadiene thus far reported in the literature have not exceeded +1° C. Varying values have been reported, both because of sample variations (differing amounts and distributions of chain imperfections) and because of variations in experimental techniques used to measure the melting point (in particular, varying heating rates). Some workers have extrapolated their data to predict that the melting point of a perfectly regular (100 per cent cis) cis-1, 4- polybutadiene (Tm°) would be close to +1° C. These extrapolations have been used to arrive at heats of fusion for the polymer from Flory's theory for melting point depression due to copolymeric impurities. One such value has been used in another investigation to estimate extents of crystallization from thermodynamic data. We wish to report observation of melting points several degrees higher than the assumed Tm° value of +1° C. Our experiments show that these higher values are not due to orientation effects.