bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction of Creep Behavior from Stress Relaxation Data for Nonlinearly Viscoelastic Materials
Authors: Wu L. M. , Meinecke E. A. , Tsai B. C. 
Published: February 2011

Abstract
The stress relaxation behavior of many polymeric materials can be expressed in a very simple fashion, because the logarithm of nominal stress fi(t) (based upon the undeformed cross-sectional area of the sample) plotted against the logarithm of time, t, is a straight line. Furthermore, these lines are often parallel, and with linearly viscoelastic materials, one obtains a straight line for the stress-relaxation modulus E(t)=fi(t)/εi, independent of the strain level. Thus, the linear stress-relaxation modulus can be expressed as: Ei(t)=Ei0·t−m, with Ei0 the modulus at t=1 s and m the slope of the straight line in the double logarithmic plot. Most polymers are, of course, nonlinearly viscoelastic (except for infinitesimal deformations); that is, the stress-relaxation modulus is a function of both time and strain. These time and strain effects can be factored out, if the log fi(t) versus log t curves are parallel: Ei(t,εi)=Ei0·t−mϕ(ε), where ϕ(ε), the strain function, is a measure of the nonlinearity of the viscoelastic response. It has been shown elsewhere that Ei0/ϕ(ε) is approximately identical to the modulus observed in the stress-strain measurement. With many polymers, creep experiments also yield approximately straight lines of slope n, when the logarithm of strain εi(t) is plotted against the logarithm of time. With nonlinearly viscoelastic materials, one generally does not obtain a set of parallel lines, when the stress fi, is changed. Therefore, it is not possible to separate the influence of time and stress on the creep compliance Di(t)=εi(t)/fi, as was the case for stress relaxation. It has been shown previously that the creep behavior can be predicted from stress-relaxation data with the help of the convolution integral. The numerical method involved is very laborious, however. It has been shown that the rate of creep may be predicted from the slope of stress-relaxation curves and the shape of the stress-strain curve. The purpose of this paper is to present a method by which the creep behavior of nonlinearly viscoelastic materials can be predicted in a simple fashion from stress-relaxation data. The theoretical predictions have been tested with the stress-relaxation and creep data of a block copolymer.
The Use of Rubber for Impact Protection in Automobiles
Authors: Leaver A. D. W. 
Published: February 2011

Abstract
The requirement that cars should be protected from impacts has led to the adoption of new designs of rubber components and new compounds. There is great scope for designers and engineers to use impact-absorbing rubber units, high-modulus vulcanizates, and paintable rubbers in a wide variety of applications in the automobile field and elsewhere.
Characterization of Tire Emissions Using an Indoor Test Facility
Authors: Williams R. L. , Cadle S. H. 
Published: February 2011

Abstract
A tire emission facility has been built in which several tire-wear modes can be simulated while the gaseous, airborne particulate, and sedimentary particulate emissions are collected. The facility was shown to produce tire temperatures and wear rates typical of operating tires. This approach to tire-emission research has many advantages over previous attempts to study tire emissions. The emission rate of gases and airborne particulate matter was nearly independent of wear rate and accounted for only 1–20% of the total emissions. The balance of the emissions were large particles which would be expected to settle on or very close to roadways. Chemical analysis of these large particles showed that approximately 30% of the SBR is unvulcanized, compared to only 1–2% in the tread. The total organic content of the particles was unchanged. This degradation of the rubber leads to enhanced oxygen absorption rates. However, the full significance of the increased rate of oxidation is not known.
Synthesis and Dilute-Solution Behavior of Model Star-Branched Polymers
Authors: Bauer B. J. , Fetters L. J. 
Published: February 2011

Abstract
The occurrence of polymers branched in a random fashion is common. Chain transfer reactions can cause short- and long-chain branching in polymerizations such as the high-pressure polymerization of ethylene. Branching can also be introduced intentionally by the use of a polyfunctional monomer in end-linking polymerizations. Similar branching can be produced in addition polymerizations by the use of a small amount of difunctional monomer, e.g., divinylbenzene. There also has been much interest in graft polymerization by which long chain branches can be introduced onto a backbone, which is often a different polymer from the branches. The properties of branched polymers can be quite different from those of linear polymers of the same molecular weight. For example, bulk viscosities as well as concentrated and dilute solution viscosities can be lower for branched polymers than for a linear material of equivalent molecular weight. As an example, the melt processing behavior of polymers can be manipulated by alterations in the average molecular weight, molecular weight distribution, and the frequency and length of long branches in the molecules. Thus, there is an obvious need to correlate and characterize the type and degree of branching in a polymer with its effect on the physical properties in solution or melt. In all of the above examples of branching, there is a mixture of branched and unbranched material. The unbranched and branched polymers can have a wide molecular weight distribution, as can the branches themselves. Also, the frequency of branches and the segment lengths between branch points can vary. Hence, the physical properties of such materials represent an average of the properties of all the different species present.
Cord—Rubber Tire Composites: Theory and Applications
Authors: Walter Joseph D. 
Published: February 2011

Abstract
The stiffness and strength behavior of the constituent cord and rubber components of the pneumatic tire have been studied in detail by investigators in the industry since the early days of tire production. For example, the effect of twist on the stress-strain properties of cotton tire cord and the reinforcing effect of carbon black on the modulus of natural rubber were well known phenomena many decades ago. Similarly, differences between the elastic and viscoelastic behavior of cord and rubber have been well documented since the 1940's. On the other hand, the material properties (specifically, the elastic constants) of the cord-rubber composite system that comprises the tire are not as well known and have only begun to receive serious attention in the last decade. These tire elastic properties, whether they be referred to as stiffnesses, compliances or moduli, are anisotropic—i.e., they vary with direction. It is the properties of the anisotropic cord-rubber composite that primarily control the overall performance characteristics of pneumatic tires. Yet, much of present day tire design has been dominated by the separate influences of rubber compounding and textile technology. This situation has arisen perhaps because the functions of the individual cord and rubber components of the tire are well known, at least qualitatively; the low modulus, high elongation rubber contains the air and provides abrasion resistance and road grip; the high modulus, low elongation cords provide reinforcement for the rubber and carry most of the loads applied to the tire in service. However, it is shown later in this discussion that, in order to optimize a given tire performance parameter, a knowledge of the combined cord-rubber composite material properties is required. For example, the crown angle for maximizing the tread wear resistance for a steel-belted radial tire is not the same as for a rayon-belted radial of the same size. While this fact could be empirically established by “trial-and-error” tire building and test methods, such a program involving the wide variety of available tire cord and rubber compounds would be time consuming and expensive. Thus, composite material mechanics, even though in its early stages of development as far as cord-rubber systems are concerned, can and should be used to economically investigate the technical merits of potential tire designs.
Total Thermal Analysis of NBR Vulcanizates
Authors: Sircar A. K. , Lamond T. G. 
Published: February 2011

Abstract
NBR vulcanizates of different nitrile content can be identified by total thermal analysis. Vulcanizate composition analysis is complicated because of formation of carbon from NBR. The difficulty can be obviated by identifying the specific type of NBR by Tg and making allowances for the known amount of carbon formation for that specific type.
N-(Morpholinothio)Imides as Curing Agents in Semiefficient Vulcanization Systems
Authors: Son P. N. , Krueger R. A. 
Published: February 2011

Abstract
It is well known that both the thermal and oxidative aging characteristics of vulcanizates can be improved by using an efficient vulcanization (EV) or semi-EV system. These desirable aging properties are attributed to the presence of mono- and disulfidic crosslinks in the vulcanizates cured by EV or semi-EV systems. In contrast to a polysulfide crosslink, mono- and disulfide crosslinks are more thermally stable and undergo minimal crosslink modification during aging. One way to achieve such desirable properties is to cure a stock with 2-benzothiazyl 4-morpholino disulfide (BMD) and low levels of sulfur. However, the BMD cure system lacks the scorch protection required for many applications. Moreover, neither N-(cyclohexylthio)phthalimide (CTP) nor N,N′-bis(cyclohexylthio)oxanilide (BCTO) shows an appreciable effect on the scorch time of BMD cure systems. This is true regardless of the level of sulfur used, as shown in Figure 1. The maximum increase in scorch time with 1.00 part CTP was only 35%, and this occurred only when three parts of BMD and no free sulfur was used. When 2.00 parts sulfur was used, scorch time was extended only 18%. Likewise, BCTO did not respond well in BMD cure systems. The poor performance of these retarders in BMD cure systems prompted us to design a cure system in which BMD can be formed during vulcanization.
Effects of Processing Variables on the Mechanical Properties of Carbon Black Filled Rubber
Authors: Wijayarathna B. , Chang W. V. , Salovey R. 
Published: February 2011

Abstract
Vulcanizate properties such as tensile strength, abrasion resistance, and tear resistance, are often enhanced by the introduction of structural heterogeneity. This is usually achieved by incorporating fillers into the polymer matrix. In addition to the type of filler and polymer used, mechanical properties depend on factors such as filler particle size, distribution, filler-polymer interaction, and network homogeneity. These factors are largely governed by the conditions of the mixing. The most widely used filler in rubber is carbon black. Carbon black, produced by the pyrolysis of hydrocarbons, is in the form of fused primary aggregates which flocculate to form large secondary aggregates held together by van der Waal forces. The term structure, as applied to carbon black, commonly refers to both primary and secondary aggregates and is designated as primary or secondary structure. The reinforcement of rubber by carbon black depends considerably on the particle size and structure of the black used. Voet and associates have shown evidence that the primary structure is not broken down by shearing action during mixing. However, Heckman and Medalia and Gessler claim that fracture of the primary structure could result from severe mechanical shear. The general consensus is that breakdown of the primary structure of carbon black is not extensive in the usual mixing process. Boonstra and Medalia, among others, reported that large agglomerates remaining after insufficient mixing have a deleterious effect on the rupture properties of vulcanizates. Hence, an optimal mixing process does not destroy secondary aggregates. The secondary structure plays an important role in the dispersion of carbon black during mixing as rubber is squeezed into both primary and secondary aggregates. Low structure blacks pack much more tightly than high structure ones and are more difficult to disperse.
Differentiation of Natural and Synthetic Polyisoprene by Combined Derivative Thermogravimetry and Gas Chromatography
Authors: Brazier D. W. , Schwartz N. V. 
Published: February 2011

Abstract
A major objective of this study was to develop a general method by which NR and IR can be differentiated and quantitatively determined in unknown vulcanizates. From the above data, it is apparent that none of the thermal analysis methods—DTG, DSC or DTG-GC—can give an unequivocal answer alone, unless the type and loading of carbon black, the sulfur level and the accelerator system of the unknown compounds are known. The general type of carbon black can be determined using a recently published DTG method, and the loading is readily determined by DTG or an ashing experiment. Determination of the exact accelerator system remains a problem. The limitations of each method can be summarized: (1) The DTG thermogram will differentiate NR and IR provided the sample is vulcanized and contains carbon black. (2) The DSC will differentiate NR and IR on the basis of the observed exothermic heat, provided the sample is vulcanized. (3) In DTG—GC, the appearance of dimethylethylbenzene in the distillate is indicative of the presence of IR. For all vulcanized IR compounds, the presence of dimethylethylbenzene is accompanied by a low isoprene/3-methyl-cyclohexene yield. For the analysis of NR:IR blends, calibration curves such as those shown in Figure 7 can be constructed, but the above limitations still apply, i.e. filler loading and type, sulfur level, and accelerator system must be known.
A New Sulfur Modified Polychloroprene
Authors: Schmitt S. W. , Anolick C. 
Published: February 2011

Abstract
Among commercial polychloroprenes, mercaptan modified types cured with thioureas have yielded vulcanizates with the best heat aging and compression set properties. In contrast, sulfur modified polychloroprenes have been inferior in these properties, but superior in hot strength, resilience, and resistance to flexing and tear. In the past the polychloroprene user was forced to choose between the two contradictory sets of properties. A new sulfur modified polychloroprene has been developed which eliminates this compromise. The new product can be cured with metal oxides alone. The vulcanizates have better tear strength than previously obtainable; resilience, flex resistance, and heat aging equal to the best previous; and compression set resistance approaching that of mercaptan modified polychloroprene cured with thioureas. This combination of properties was not available heretofore. Although accelerators are not normally required, the cure cycle of the new polychoroprene product can be modified by conventional techniques.
Vulcanization of a Fluoroelastomer Derived from Tetrafluoroethylene and Propylene
Authors: Kojima G. , Wachi H. 
Published: February 2011

Abstract
An effective vulcanization recipe for tetrafluoroethylene-propylene elastomer was searched for and the following results were obtained: (1) The C2F4-C3H6 copolymer is susceptible only to peroxide and is not crosslinked at all by other reagents. (2) The peroxide vulcanization is greatly accelerated by some coagents, and triallyl isocyanurate was found to be the best cure promoter. (3) The vulcanizate obtained by using a combination of α,α′-bis-(t-butyl-peroxy)-p-diisopropylbenzene with triallyl isocyanurate as curative exhibits good mechanical properties together with excellent heat and chemical resistance. (4) The mechanism of the vulcanization reactions seems to involve a chain reaction which greatly increases the efficiency of the vulcanization reaction by the peroxide.
Thermo-Oxidation of Elastomers by Differential Scanning Calorimetry
Authors: González Virgilio 
Published: February 2011

Abstract
Using the DSC technique it is possible to evaluate the efficiency of antioxidants in rubber, using the increase in Ti of the rubber on adding antioxidant in a known concentration. The creosote bush resin chloroform extract is more efficient in synthetic than natural rubbers. The increase in Ea can be explained by the formation of peroxy-quinolinic intermediates in the slow stage of the reaction and it is possible to calculate the Ea based on this same increase, when the relationships between the reaction and Ti, and between Ea/N calculated by Gorbachev and Ti, are known. These are given for Hr=10°K/min using Equations (7) to (11), which greatly simplifies calculations and reduces experimental tests.
Fluoroelastomer Polymers—Compounding and Testing for Downhole Environments
Authors: West A. C. , Ray T. W. 
Published: February 2011

Abstract
A laboratory screening test simulating sour gas downhole conditions has been developed that provides directional information on the factors that control elastomer seal performance in this harsh environment. The results of this test have been correlated to environmental testing of O-rings in simulated downhole conditions using sour crude oil at 203°C and evaluating the pressure failure over the range of 69 MPa to 138 MPa. The results of this testing program have demonstrated the factors that affect overall seal performance for commercially available fluoroelastomer raw gums in downhole environments in the following order of importance: 1. a vulcanized compound modulus at 50% elongation of greater than 6.9 MPa, 2. cure type order of preference of peroxide &gt; bisphenol &gt; diamine, 3. increases in fluorine level from 65 to 69 weight percent have little effect on seal performance in conditions evaluated, and 4. the compound hardness is not as important a factor in predicting compound failure or success as is molecular weight selected that results in elongation of 70–100% at high filler loadings to achieve high modulus. The laboratory screening/environmental testing sequence reported here has proven successful in predicting fluoroelastomer properties necessary to manufacture seals for actual downhole service.
The Effect of Oxidized Fuel on Polymers
Authors: Trexler Harold E. 
Published: February 2011

Abstract
Some polymers exhibit exceptional resistance to oxidized gasoline as evidenced by minor changes in their tensile and elongation after aging in the oxidized fuel for 1008 hours at 40°C. The polymers with the smallest changes in properties are TFE and polyamide plastics and TPE thermoplastic elastomer followed by PNF, AU-2D, and FKMF elastomers. Other materials which also have good resistance to oxidized gasoline and should be considered for further development in oxidized fuel applications include: FVMQ, FKMV and NBR P-684 elastomers and TPPE thermoplastic. Aging in oxidized diesel fuel generally causes less change in properties of polymers than aging in oxidized gasoline. For this reason, candidate polymers for oxidized gasoline applications will also function well in oxidized diesel fuel.
Vulcanization of Guayule Rubber
Authors: Ramos-De Valle L. F. 
Published: February 2011

Abstract
The vulcanization characteristics of natural guayule rubber (GR) were compared to those of natural hevea rubber (HR). In the case of purified rubbers, vulcanization and tensile properties were shown to be very similar, whereas in the unpurified raw rubbers, HR was faster in vulcanization and attained a higher modulus than GR. These differences between raw rubbers were most pronounced in conventional vulcanization systems using MBT as the sole accelerator. As a result of a variety of different types of measurements on raw and purified rubbers, (relaxed tensile stress [MOD], Monsanto Rheometer curves, degree of crosslinking measurements, and kinetic analysis) it was concluded that the differences between HR and GR were due to the natural occurrence in HR (and absence in GR) of a vulcanization activator of a type similar to a basic secondary accelerator. Finally, in any formulation, the addition of very small quantities of activator or basic secondary accelerator is recommended in GR in order to attain similar properties to those of HR.
Long Chain Branching in Natural Hevea Rubber-Determination by Gel Permeation Chromatography
Authors: Angulo-Sanchez J. L. , Cabaulero-Mata P. 
Published: February 2011

Abstract
The hevea brasiltensis rubber contains, besides the insoluble branched entities, linear and branched molecules in the soluble fraction. The branching characteristics found by analyzing fractions of different molecular weight of rubber coagulated from freshly tapped latex, stabilized with hydroxylamine hydrochloride are: (a) molecules with molecular weights above 6.5×104−1.0×105g/mol (depending on the branch points functionality) are branched and molecules below these limits are linear. (b) The relationship between number of branch points and the logarithm of molecular weight is linear. (c) The branching density is not independent of molecular weight, as has been assumed for several polymers, but it has a maximum. The maximum branching density found in the soluble fraction is between 10.2×10−6 and 31.6×10−6mol/g, which varies little with the molecular weight; it is possible that molecular species with higher values become insoluble. (d) Branching results ˜λ and gel content (36%) of the whole rubber gave a total of 93–98% of branched entities (sol and gel) and 2–7% of linear species.
Significance of Extensional Flow in Processing of Rubbers
Authors: Cotten G. R. 
Published: February 2011

Abstract
Simple shear is the customary mode of deformation for the study of rheology. Simple shear measurements can be done by means of a variety of laboratory instruments such as shearing disks, concentric cylinders, or capillary rheometers. The results so obtained have been successfully used to predict the flow of fluids through tubes and some more complex processes, like extrusion and certain aspects of mixing. However, simple shear experiments do not provide all the information necessary to describe processability of polymers. In particular they are totally unrelated to phenomena of extrusion shrinkage (die swell), extrusion appearance (melt fracture), or crumbling on the mill. A better understanding of these phenomena can be obtained by examining polymers in simple extensional flow.
Rubber-Thermoplastic Compositions. Part III. Predicting Elastic Moduli of Melt Mixed Rubber-Plastic Blends
Authors: Coran A. Y. , Patel R. 
Published: February 2011

Abstract
Blends prepared by mixing rubbers with plastics in the molten state have been known and used for a number of years. The stiffness of such blends vary widely with both the proportions of rubber to plastic and with material selection, even at equivalent rubber to plastic proportions. This report describes correlations between blend stiffness and the properties of the individual blend components. Dynamic shear modulus G′, determined by torsion pendulum measurements, was used to characterize the stiffnesses of the blends. Values of G′ were related to the moduli of the hard and soft (plastic and rubber) phases, G′H and G′S, and the volume fraction of plastic ϕH through a single adjustable parameter by means of a recently proposed relationship. The adjustable parameter was then correlated with other properties of the blend components. In contrast with the work reported in the first two papers of this series, this report is on compositions in which the rubber is not crosslinked.