bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations on the Tearing of Elastomers
Authors: Stacer R. G. , Yanyo L. C. , Kelley F. N. 
Published: February 2011

Abstract
1. Frequency distributions of stick-slip tear arrest and initiation energies have different standard deviations; initiation values show greater variance. Tear arrest frequency distributions are symmetrical and have been described by a normal distribution. The tear-initiation distribution is skewed and has been modeled using both the extreme value and Weibull distributions. As a result, it is concluded that two separate mechanisms are responsible for the creation of the force minima and maxima observed in stick-slip tearing. Consequently, data reduction methods which average these values to estimate tear energy are inappropriate. 2. The direction of skewness of the tear-initiation energies indicates a distribution of the largest extreme. This has been contrasted with constant-rate tensile-rupture data which are distributed according to the smallest extreme. As a result, it is concluded that the process responsible for tear initiation is not a weakest link mechanism, but, rather, depends on a process which structurally inhibits tear propagation. A mechanism of anisotropic tear-tip reinforcement caused by large regional deformation has been discussed as a possible explanation. 3. Tear energies calculated from tear-initiation forces have been shown to be dependent upon the energy stored in simple tensile extension and the volume of material available to be extended. This type of behavior shows that the tear-initiation energy is perhaps a reasonable indicator of strength but does not meet the criterion for an inherent material property. Tear-arrest values have been shown to be independent of these features and are considered unbiased estimators of inherent material tear energies. 4. It has been shown that for experimental purposes, stick-slip tearing can be eliminated and tear-tip diameter can be held constant using a constrained trouser-tear test. This is in agreement with earlier work by Gent and Henry. It has also been shown that the constrained tear energy thus measured is an inherent feature of stick-slip tearing results, requiring only additional data reduction to extract. Consequently, the constrained tear energy can be estimated from stick-slip tearing, and conversely, the magnitude of stick-slip tearing is predictable from a constrained tear energy and simple tensile extension data.
Heat Transfer and Property Development in Liquid Silicone Rubber Molding
Authors: Macosko Christopher W. , Lee L. James 
Published: February 2011

Abstract
This study has used a heat transfer model to describe the cure of liquid silicone rubbers. The model shows that cure always starts from the wall and will continue during cooling. Thick parts may not be totally cured upon demolding, although the material near the wall has reached a desirable mechanical strength. Since silicone rubbers gel fast at high temperature, mold filling problems may occur for the thin and long molds, especially at high mold temperatures.
Failure of Rubber by Abrasion
Authors: Pulford Carl T. R. 
Published: February 2011

Abstract
This short review presents the landmark discoveries and ideas in rubber abrasion that have brought the field to where it is today. First, the important features of rubber abrasion are reviewed as background for a physical model for the abrasion of rubber. The model, due to Thomas, is described in detail, since it clearly shows the connection between the failure of rubber by abrasive wear and the appropriate rubber fracture properties. The implications of the model for improved abrasion resistance are also discussed. Then, physical principles are applied to the failure of rubber by abrasion in actual products, such as tires. The tire wear model of Schallamach and Turner is described, together with its success in explaining several features of tire wear.
Rubber Enters the Polymer Age
Authors: Morton Maurice 
Published: February 2011

Abstract
I hope that this review of the highlights of my research and educational activities over the past 40 years has demonstrated how polymer science has taken over the fairly “ancient” art of rubber technology; and how both the methods of research used in and the career training required for man's utilization of this unique material are now firmly established as part of the science of macromolecules.
The Action of Antiozonants in Rubber
Authors: Brück D. , Königshofen H. , Ruetz L. 
Published: February 2011

Abstract
Rubbers with olefinic double bonds, and rubber goods based on them, are destroyed by ozone. Crack formation can be retarded by adding antiozonants. The mechanism of the antiozonant effect has not yet been fully explained. The mechanism by which bis-(1,2,3,6-tetrahydrobenzaldehyde)-pentaerythrityl acetal (AFS), a nonstaining antiozonant, hinders the ozonation of polychloroprene has been described. AFS competes with the double bonds in the polymer for the available ozone. Additionally, the resulting ozonization products prevent the ozone from penetrating into the polymer matrix. This mechanism was corroborated by carrying out kinetic measurements of the competing reactions in solution and in the rubber. The findings were confirmed by studying model substances with basic structures identical to AFS but with modified active groups.
Internal Mixing: A Practical Investigation of the Flow and Temperature Profiles during a Mixing Cycle
Authors: Freakley P. K. , Patel S. R. 
Published: February 2011

Abstract
From the results of mixing trials with a highly instrumented BR Banbury and biconical rotor rheometry of mixed batches, a detailed analysis of flow and mixing characteristics in the region of a rotor wing has been undertaken. An ‘angled spreader blade’ analogy of the rotor wing is proposed as being a viable basis for mathematical modelling. A one-dimensional flow analysis is used, in which power-law flow behavior and isothermal conditions are assumed. Dispersive mixing, which depends on the stress levels generated during mixing, is shown to occur throughout the entire mass of material swept in front of the rotor wing and not simply at the rotor tip. In addition, the stress levels depend more strongly on batch temperature than on rotor speed. High rotor speeds tend to lead to reduced stress levels as a result of the associated rapid rise in batch temperature, although choosing an appropriate fill factor can minimize temperature rise by promoting efficient heat transfer to the cooling water. During each rotor revolution, the rotor wing collects a mass of material from the reservoir between the rotors. This mass of material is then progressively reduced by leakage flow under the rotor tip and flow around the end of the wing, until the revolution is completed by the return of a residue to the reservoir. The flow around the end of the rotor is shown to be consistently greater than the leakage flow, although the ratio can be influenced by both fill factor and rotor speed. At high rotor speeds and low fill factors, it appears that material is retained in the regions of the side frames of the mixer and may give batch inhomogeneity through poor distribution mixing.
Mixing of Carbon Black with Rubber. II. Mechanism of Carbon Black Incorporation
Authors: Cotten George R. 
Published: February 2011

Abstract
The present study leads to postulating the following mechanism for carbon black incorporation. During the first stage of incorporation, carbon black agglomerates become encapsulated by the polymer. At this stage, the interstices within these agglomerates are still filled with air, giving a very weak, crumbly composite. The rubber becomes forced into these interstices during the second stage of incorporation. As the rubber is being forced through the narrow channels between the aggregates, bound rubber is being formed. The immobilized layer of the polymer tends to reduce the effective cross section of the channels through which more rubber must pass before reaching the inner part of the agglomerates. Thus, as the activity of carbon black increases, e.g., higher bound rubber, the incorporation time increases. At a given carbon black activity, the effective thickness of the immobilized polymer layer would increase with increasing molecular weight of polymer, but be independent of the oil loading. This agrees with experimental observation that the incorporation time increases with molecular weight of the polymer, while oil loading has no effect other than that associated with the lowering of bound rubber content. The average size of channels through which rubber must pass depends also on the carbon black morphology. The size of these channels would be expected to increase with increasing structure of carbon black, and (to a lesser extent) with increasing particle size. These parameters have the expected influence on the incorporation time; since the incorporation time decreases with increasing DBPA value and decreasing tint.
Dynamic Property and Fatigue Crack Propagation Research on Tire Sidewall and Model Compounds
Authors: Young D. G. 
Published: February 2011

Abstract
Research was conducted to define appropriate compound loading conditions and energy parameters required to properly control and analyze fatigue crack propagation experiments for tire sidewall applications. The effects of strain level, pulse frequency, overall cycle frequency, sample thickness, and oven temperature were screened, and strain level was shown to be the dominant variable in the region of interest. Designed experiments further confirmed that frequency (i.e., strain rate) effects upon strain energy are small at normal rates of tire deformation (equivalent to 40 Hz). However, at typical laboratory test frequencies (≤5 Hz), strain rate effects on strain energy are large, and the differences vs. results under tire conditions depend heavily on polymer type as well as test temperature. Thus, the use of strain level, strain rate, and temperature conditions which simulate the tire service environment are critical to give representative results in laboratory testing. A constitutive equation was defined which provides an excellent model for strain energy in pure (or simple) shear as a function of the principal extension ratio (i.e., strain level) at constant frequency. Therefore, computer modeling of such experiments appears straightforward using an on-line minicomputer. Fatigue crack propagation studies showed major effects of pure-shear sample thickness, processing prior to molding, different types of reference compounds, and different polymer types. Halobutyl compounds and halobutyl/EPDM/NR blends were shown to provide superior FCP resistance at a given strain or strain energy level. These results were consistent with earlier tire and laboratory data.
Defect Accumulation in Rubber
Authors: Roland C. M. , Smith C. R. 
Published: February 2011

Abstract
It has been demonstrated that the material adjacent to the fracture plane in cured rubber specimens can scatter intense x-ray radiation at small angles. This phenomenon is associated with the presence in the material of voids of very small size. These microvoids exist only adjacent to the fracture surface and are the result of the loading imposed to create the macroscopic fracture. The significance of these microscopic defects is their influence on the manner in which externally applied loads produce fracture of rubber; that is, they provide a link between the experimentally observed fracture behavior of rubbers and the fundamental processes governing this behavior. To cite a few examples, it has been observed that the critical value of tearing energy required for catastrophic failure of a rubber specimen differs for a static versus dynamic mode of deformation. It can be recognized that these differences are related, not only to rate effects, but also to the differences in the state of the fractured material directly in front of the crack tip. It has also been noted that the manner in which one introduces a precut into a rubber test specimen can influence the ensuing strength measurement by affecting the nature of the initial fracture plane. It should be understood that the test result can be affected not only by such differences in the geometry of the precut, but as well by the effect the precutting can have on the condition of the unfractured material adjacent to the precut. Currently, our efforts are being directed towards modification of the SAXS instrument to permit measurements to be made at lower values of scattering angle. It is hoped that this will allow quantification of the size and abundance of the microcracks. Such information can provide insight into the significance of defect accumulation in the development of tear resistance in elastomers.
Rubber-Thermoplastic Compositions. Part IX. Blends of Dissimilar Rubbers and Plastics with Technological Compatibilization
Authors: Coran A. Y. , Patel R. , Williams-Headd D. 
Published: February 2011

Abstract
From this work, one can conclude that compositions which have excellent mechanical properties can be prepared by melt-mixing thermoplastic vulcanizates. (A thermoplastic vulcanizate is a composition containing vulcanized rubber particles dispersed in a thermoplastic. Such a composition is usually prepared by vulcanizing the rubber during its melt-mixing with a thermoplastic.) The excellent mixed TPV compositions can be obtained even though the rubbers and plastics are mutually grossly incompatible with respect to thermodynamic considerations. In such cases, however, it appears to be necessary that a compatibilizing agent be present in the mixture to promote the interaction between the thermoplastic materials. Block copolymers whose molecules contain blocks common to each of the thermoplastic blend components are good technological compatibilizing agents (e.g., polypropylene-nylon block copolymers to compatibilize mixtures containing polypropylene and nylon). Compatibilizing block copolymers can form in situ during melt mixing. This appears to be the case when one of the thermoplastic blend components is functionalized to chemically link with another thermoplastic component of the mixed TPV composition. The rubber associated with one thermoplastic can differ greatly from the rubber associated with another thermoplastic component of the mixed TPV blend. Thus, a composition which has good mechanical properties can contain both differing thermoplastics and differing rubbers. As a result, the possible combinations of components for TPV compositions has been greatly expanded.
Relationship between the Cohesive Strength and the Tack of Elastomers: Part II, Contact Time Effects
Authors: Hamed G. R. , Shieh C-H. 
Published: February 2011

Abstract
The self-tack (also called autohesion or simply tack) of an elastomer is its ability to resist separation from another piece of the same elastomer compound with which it has been brought into contact for a short time under a light pressure. Briefly, the events that take place in the interfacial region to form the tack bond are: 1) the attainment of intimate molecular contact of the polymeric chains from each surface; this requires viscous flow of the material near the surfaces and displacement of any impurity that may prevent contact, and, 2) interdiffusion of chains across the (temporary) interface; shorter chains will diffuse more rapidly. If the two contacted elastomeric layers are uncrosslinked, then the interface between them will eventually disappear and the strength of the junction (tack bond) will become identical to the cohesive strength of the material. This process has been referred to as “healing”. It is instructive to define relative tack as the measured value of tack (given, e.g., by the force to peel apart two contacted elastomeric strips) divided by the cohesive strength of the material determined in the same test geometry. Relative tack can have a value between zero and one. When the value is near zero, then it is inferred that the degree of interfacial contact and/or interdiffusion is quite incomplete. On the other hand, when the value approaches unity, the tack bond behaves as though the junction were completely healed. A very important feature of relative tack is that, even for a given time and pressure of contacting, its value is not unique, but depends markedly upon the test conditions selected to pull the bond apart. This interesting behavior was shown in a previous publication. Specifically, relative tack is rate dependent such that it may have a low value at some test rates (indicating only partial healing), but be equal to one at other test speeds—in spite of incomplete interfacial fusion. In this earlier investigation, measurements were carried out on specimens that possessed only a single extent of healing, i.e., the contacting conditions (time and pressure) were held constant. In this paper (Part II), studies of the rate and temperature dependence of bond strength are extended to include tack bonds possessing varying degrees of healing. This was simply achieved by varying the contact time before measuring tack.
Auger Electron Spectroscopic Analysis of Dispersants in Rubber
Authors: Lin Sin-Shong 
Published: February 2011

Abstract
Auger electron spectroscopy is a versatile tool in studying the chemical constituents of dispersions in rubber. This technique combined with the SAM analyses produces two dimensional images which are useful in the elucidation of aggregations and dispersion states of the rubber additives. Especially, particle inclusions and agglomerations can be studied together with the topographic features of the complementary SED image. Additional information concerning the binding states of elastomers and additives, aggregations of excessive crosslinkages, unsaturated double bonds, and large hard segments of polymers can be imaged with the aid of chemical reactants. The success of the present AES technique depends on the proper preparation of sample surfaces. A conductive surface is an essential factor in the analyses of additive dispersions. The heating of the surface by the electron beam, as well as the alternation of the surface topology by electron specimen interactions, should also be considered in the correct interpretation of the observed images. Artifacts associated with the analysis should be carefully examined so that they might reveal information about the composition and heterogeneity.
Chain Conformation in Elastomeric Multiblock Copolymers as Measured by Small-Angle Neutron Scattering
Authors: Cooper Stuart L. , Miller John A. 
Published: February 2011

Abstract
Small-angle neutron scattering has been shown to be an effective technique for investigating segment conformation in two-phase multiblock copolymer systems. By choosing the appropriate isotopic compositions, either segment can be investigated, as can the whole chain. The best approach to the experiment is to use a phase-contrast matched sample, one where no interphase scattering occurs. This allows the experiments to be carried out on a single sample, simplifying the experiment, and reducing the beam time requirements. Equations (2) and (3) describe the phase-contrast matched criterion. At room temperature, the polyether soft segments in the polyurethane elastomer-and in the polyether-polyester block copolymers are somewhat extended on the average relative to the bulk oligomer conformation. In the polyether-polyester with a lower hard-segment content, the soft segments are less extended than in the higher ester content material. A distribution of conformations occurs in these materials, with a majority of the soft segments being nearly in a random-coil conformation. A substantial number of segments are fairly taut, leading to an average conformation that is somewhat extended relative to the random coil conformation. The soft-segment radius of gyration in the polyurethane material initially decreases with increasing temperature. As the temperature rises, the retractive force on the taut soft segments increases, thus facilitating the extraction of hard segments from the amorphous hard phase into the soft phase. One would expect that the degree of phase separation would decrease with increasing temperature due to such a mechanism, and in fact this is borne out by small-angle x-ray scattering studies. Above 150°C, an upturn in the soft-segment radius of gyration is observed. Koberstein et al. propose a phase mixing transition around this temperature in polyurethane systems. Such a transition implies a greater compatibility between the hard and soft segment types at elevated temperatures. Thus, a swelling of the soft segments is seen due to favorable interactions with the hard segments located in the soft phase. A schematic diagram of the polyurethane microstructure and chain conformation is presented in Figure 9. The soft-segment radius of gyration in the polyether-polyester materials decreases smoothly with increasing temperature. This is primarily due to a decrease in the number of taut tie molecules present at elevated temperatures due to the rearrangement of the hard crystalline domains. In addition, relaxation of stresses introduced by molding these samples below the hard-segment crystalline melting temperature may contribute to the decrease in the soft-segment Rg.
Novel Wet Process Silica Prepared from Alkyl Silicates. Part III: Use in Silicone Elastomers for Optical Applications
Authors: Polmanteer Keith E. , Chapman Harry L. , Lutz Michael A. 
Published: February 2011

Abstract
The first two papers of this three-part series of papers dealing with a novel wet-process hydrophobic (WPH) silica technology covered the silica synthesis (Part I) and reinforcement performance (Part II) respectively. The WPH silica was highly reinforcing and provided optically clear compositions as well. The first optically clear, high consistency silicone elastomer was developed in the midnineteen fifties by Polmanteer et al., using different technology from that described in this paper. Optical clarity was accomplished in the earlier work by matching the refractive indices of the filler and polymer at 25°C, making them isorefractive at this specific temperature. This paper will discuss the unique features of this new silica technology as it relates to optically clear silicone elastomers. The term, optically clear, in the context of this paper refers to an elastomeric material, 2.54 mm in thickness, that exhibits less than 4% haze, and more than 85% transmission. It will be shown that, when using the older technology based on isorefractive compositions, optical clarity is reduced with temperature change from the isorefractive temperature, due primarily to an increase in haze. The new silica technology eliminates this problem and effectively broadens the application temperatures for optically clear, thermally stable silicone elastomers.