bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoplastic Polyurethane Elastomer Melt Polymerization Study
Authors: Schollenberger C. S. , Dinbergs K. , Stewart F. D. 
Published: February 2011

Abstract
It is concluded from the present study that the slightly modified Brabender PlastiCorder torque rheometer is well suited to the study of thermoplastic polyurethane elastomer melt polymerization. The instrument is sensitive and responsive enough over a broad range to sense and record continuously even small changes in polymerizate temperature and viscosity as a function of time. This capability has enabled us to follow the full course of such polymerizations, with the exception of the final polymer maturation process which customarily is effected in the quiescent state. In our study, the effects of several polymerization variables were clearly and quantitatively apparent, including the effects on the course of polymerization and its degree of: macroglycol acidity; antioxidant (stabilizer); temperature; catalyst; polymer composition; presence of shortstop; and reactant balance. The results demonstrate the known acid catalysis of the hydroxyl-isocyanate reaction as well as polyurethane molecular weight modification by polyester glycol acidity. The inclusion of a commercial phenolic antioxidant in the polymerization charge did not have any obvious effect on the course of polymerization but may have limited degree of polymerization somewhat. Increased urethane content greatly speeds the viscosity increase, demonstrating urethane autocatalysis as well as its viscosity contribution, and even low stannous octoate catalyst levels appreciably speeded the inherently rapid polymerization. The shortstopping action of fugitive and persistent primary alcohols is prompt and effective, but excessive amounts produce some irreversible polymer reversion as they readjust the polymer chain molecular weight distribution present in maintaining the urethane equilibrium. This equilbrium also showed clear response to polymerization temperature, reversible urethane dissociation reducing viscosity with increasing temperature. The effect of polymerization reactant imbalance was readily apparent in the appreciably reduced rate and degree of polymerization attending minor isocyanate deficiency. Mastication experiments in the PlastiCorder show dried preformed polyurethane elastomer to drop quickly to viscosity levels much below that reached by the same compositions during polymer formation. The viscosity loss of the former is attributed to polyurethane chain rupture promoted by virtual network restrictions to chain slippage, while the virtual network has not yet developed in the forming polymer.
Morphology-Property Relationships in EPDM-Polybutadiene Blends
Authors: Hamed Gary R. 
Published: February 2011

Abstract
When mixing EPDM and BR in the Brabender a heterogeneous blend results; the dispersed phase is first sheared into fibrous strands and then broken down into micron sized particles. At low doses of irradiation, the morphology of the blend only has a minor effect on the energy to break, whereas at high doses the Eb may increase by a factor of three as the dispersed particle size is reduced from the 100 micron range. The Eb of the blend is the weight-average of the two pure components at low doses (independent of morphology), but is greater than either pure component at higher doses. Interfacial adhesion may play a key role in determining the mechanical properties in rubbery blends.
Degradative Effects of Guayule Resin on Natural Rubber. II. Kinetic Studies
Authors: Keller Robert W. , Stephens Howard L. 
Published: February 2011

Abstract
Qualitative studies reported earlier and the kinetic studies reported here indicate that the unsaturated fatty acids in guayule resin are primarily responsible for the ability of guayule resin to accelerate the oxidative degradation of natural rubber. These unsaturated fatty acids apparently oxidize to form peroxide compounds which function as initiators of rubber oxidation.
Thermal Conductivity of Elastomer Vulcanizates by Differential Scanning Calorimetry
Authors: Sircar Anil K. , Wells John L. 
Published: February 2011

Abstract
A du Pont 990 differential scanning calorimeter was modified to measure thermal conductivity of elastomer vulcanizates. The method is quick and reproducible and is recommended for scouting research of polymeric materials. The thermal conductivity λ values obtained by this method of some known materials compare favorably with those in the literature. Carbon black increases λ values in all elastomers. Particle size and structure of carbon black seem to affect λ values erratically, although the trend is towards higher λ values with larger particle size and higher structure. A linear relationship of λ vs. volume concentration of carbon blacks and other fillers is observed, except at a very high concentration. The extrapolated values of λ for a filler differ in different elastomeric media. Noncompatible elastomer blends increase or decrease λ values according to the nature and proportion of elastomers. The effect of the manner of addition of carbon black does not seem to affect the λ value of compatible blends. Higher temperatures decrease λ values for all the vulcanizates studied.
Rubber-Styrene Block Copolymers in Adhesives
Authors: St. Clair D. J. 
Published: February 2011

Abstract
Rubber-styrene block copolymers are materials such as the A-B-A type block copolymers, where A represents a block of polystyrene and B represents a rubber block, usually polybutadiene, polyisoprene or an olefin rubber. Because polymers of this type form a physically crosslinked network structure, the polymers are thermoplastic as well as being strong and rubbery. Because of their unique structure, block copolymers are well suited for use in a wide variety of adhesives. Block copolymers can be formulated with resins, plasticizers, and fillers to meet performance requirements ranging from those of a soft, tacky pressure-sensitive adhesive to those of a stiff, high strength construction or assembly adhesive. Adhesives based on the block copolymers can be mixed and applied, either in solvent or as hot melts, using standard processing equipment. Research is continuing on block copolymer technology, formulating technology, and processing technology which should further expand the applications of block copolymers in adhesives.
The Use of Elastomers in Regenerative Braking Systems
Authors: Hoppie L. O. 
Published: February 2011

Abstract
Results to date on this project indicate that a regenerative braking system based on elastomeric energy storage is technically feasible, and that improvements in the elastomer further enhance the prospects of such a system. In particular, improvements in energy density are highly desirable, as this would directly reduce the required volume. Reductions in stress-relaxation rates are also desirable because less compensating is needed in the initial design. Finally, improvements in fatigue life are desirable, as this would directly increase the time between replacements of the elastomeric units. Various manufacturers and researchers have been approached to determine if an elastomer more suitable than natural rubber is available or if one is likely to be developed. The general consensus is that natural rubber is now superior to all synthetics, but suitable materials research might lead to significant improvements. No definite plans have yet been made to carry on such materials research.
Effects of Fumed Silica Treated with Functional Disilazanes on Silicone Elastomers Properties
Authors: Maxson M. T. , Lee C. L. 
Published: February 2011

Abstract
The reinforcement obtained with disilazane-treated silica in the platinumcatalyzed silicone elastomer was found to be dependent upon not only the amount of disilazane employed but also the structure of the disilazane and its distribution on the silica surface. Incorporation of a small amount of vinyl-functional disilazane such as (ViMe2Si)2NH along with (Me3Si)2NH (major treating agent) can significantly increase the modulus and hardness of the resulting elastomer. [ViMe2Si(OMe2Si)3]2NH gave higher modulus and hardness than (ViMe2Si)2NH, whereas (HMe2Si)2NH gave lower modulus and hardness values. The random treatment resulted in greater improvement of cured elastomer properties than the heterogeneous treatment at the same treatment level.
The Effects of Carbon Black-Vulcanization System Interactions on Natural Rubber Network Structures and Properties
Authors: Pal P. K. , Bhowmick A. K. , De S. K. 
Published: February 2011

Abstract
We have studied the interaction of the vulcanization system (conventional and EV) and filler (HAF black, N330) concentration on the technical properties and network structure of NR vulcanizates. At lower loadings of filler, a marked difference in values of resilience, hardness, tear strength, elongation at break and tensile strength was observed between the vulcanizates of the two systems; whereas, this difference is minimized at higher loadings of filler. At all loadings, modulus, flex cracking resistance, dynamic set, and compression set are higher for the conventional system than for the EV one. But irrespective of filler concentration, heat buildup is higher for the EV system than for the conventional system. At lower loadings of filler, abrasion loss is independent of the vulcanization system, but at higher loadings, abrasion loss for the EV system is more than for that of the conventional one. Addition of HAF black at 5 phr loading increases total crosslink density and the proportion of polysulfidic crosslinks in the conventional system, and higher loadings of filler do not have any further effect on the network structure. That is why the vulcanizates of the conventional system yield higher resilience, hardness, tear strength, elongation at break, tensile strength, modulus, flexcracking resistance, and set properties as well as less heat buildup. But at higher loadings of filler, some of the above properties tend to become independent of the vulcanization system. This implies that at higher loadings of filler, rubber-filler attachment overshadows the network structure, and the properties become independent of vulcanization system and are governed by the filler concentration. We have also calculated the vulcanization rate parameters with the help of Goran's model for understanding higher polysulfidic crosslinks in the presence of HAF black and in conventional systems.
Vibration Isolation Properties of Vulcanizates of Scrap Rubber Powder
Authors: Accetta A. , Vergnaud J. M. 
Published: February 2011

Abstract
Rubber powder recovered from old tires is recognized as a valuable raw material which may be processed into several useful products. In the cure cycles described, the rubber powder with sulfur as vulcanizing agent, with no virgin parent compound, can be converted to a useful viscoelastic material. This article is concerned with the static and dynamic vibration properties of these viscoelastic rubber materials, as well as their mechanical properties. At the optimum curing conditions (180°C, 10 min, 10 MPa), the effect of sulfur and DOP plasticizer on the vibration properties of the materials are of interest. It is possible to prepare a material, suitable for use in antivibration mountings, by choosing the right values of sulfur and plasticizer, according to the vibration characteristics of the machine, i.e., its mass and natural undamped resonant frequency.
Linear Free Energy Relationship Involving the Properties of Prevulcanization Inhibitors
Authors: Morita E. 
Published: February 2011

Abstract
The utilization of σ* constants for substituted phenyl groups converted from the known Hammett σ constants of the phenyl substituents is useful in assessing the linear free energy relationship (LFER) of the properties of various inhibitors. The inhibitors include thioketals, sulfenamides and N,N′thiobis(substituted formanilides). In the LFER of the rate of reaction between thioketals with 2-mercaptobenzothiazole, the rate is fastest when the thio group of the thioketal is attached to a substituted phenyl with the highest positive σ constant. The σ constant of alkyl groups is negative, and an alkylthio group gives a thioketal with a slower reaction rate. The LFER applies to the 13C NMR shift of the quaternary carbon of the thioketals with alkylthio groups. The slope of the linear relation is positive. However, changes in the 13C NMR shift of the arylthio derivatives are relatively small in spite of a wide variation in σ* constant. The LFER applies to the scorch delaying activities of all structural types of inhibitors in stocks accelerated by various benzothiazoles. In the linear relationship of scorch delay versus σ* constant in each type of inhibitor, the slope is negative. Variables with negative σ* constants give longer delay and those with more positive σ* constants give shorter delay. An exception is in the very fast curing MSSM/DPG stock where the thioketals from acetoacetanilide with arylthio groups give longer delay than the alkylthio compounds. In the TBBS-accelerated stock, the slopes of the linear relation of the carbamate sulfenamides, N,N′-thiobisformanilides and thioketals of cyanoacetanilides are about equal. However, the level of scorch delay obtained with the sulfenamides is significantly higher than the other two, which are equal in inhibition level. The inhibition action of N,N′-thiobisformanilides without alkylthio or arylthio groups is probably due to the formation of labile formanilide polysulfide intermediates.
An Infrared Spectrophotometric Analysis for Natural Rubber in Guayule Shrubs
Authors: Banigan T. F. , Verbiscar A. J. , Oda T. A. 
Published: February 2011

Abstract
An accurate assay of rubber content in guayule plant tissues is essential to any genetic improvement or bioregulator program. The simpler, more rapid and less expensive the assay, the better. The several methods of rubber assay that have been used have various limitations. Earlier methods for assaying rubber content in guayule are described in two USDA reports. These are principally gravimetric methods which are tedious and relatively nonselective. One of the better ones consists in bromination of the guayule double bonds, precipitation from solution, collection, drying, and weighing the crystalline rubber bromide. This bromide method is more selective for rubber in the presence of resins than the gravimetric methods where rubber is weighed directly. For multiple and repetitive analyses, it is time consuming and somewhat unpleasant due to the recommended excess of bromine. A gravimetric method reported by Tysdal in 1951 was modified recently. The method consists of grinding guayule shrub in an efficient blender with aqueous alcohol saturated with salt. The resulting slurry is screened to recover resinous rubber particles, which are dried and weighed. Precision is considered adequate for distinguishing plants of widely differing rubber content but not for detecting incremental changes. Another rubber assay of merit is the photometric method of Traub. This volumetric method depends upon a controlled precipitation of rubber particles from solution and the determination of rubber quantity by photometric measurement of the resulting turbidity. It is being used with some modifications on a guayule breeding project at the Los Angeles State and County Arboretum Research Laboratory. The principal improvement consists in extracting the rubber from the plant tissue by homogenizer milling in solvent rather than lengthy soxhlet extractions.
Accelerator Systems for Injection Molding
Authors: Paris W. W. , Dillhoefer J. R. , Woods W. C. 
Published: February 2011

Abstract
A reciprocating screw injection press has been used to evaluate various accelerator combinations in NR, SBR, EPDM, and NBR. A laboratory mold was used which includes a 75 mm × 125 mm × 2 mm sheet, three molded dumbbells (size Die C), a compression pellet and a Goodrich Flexometer pellet. The total volume of the mold is approximately 85 cm3. Those observations have confirmed that the following relationships exist for high temperature vulcanization, particularly in an injection press. (1) Tensile modulus is reduced at higher curing temperatures for all four polymer systems. (2) In NR and SBR, it is possible to obtain moduli at high temperature comparable to moduli at lower temperatures by increasing the accelerator level while maintaining a constant sulfur concentration. (3) There is a correlation between rheometer cure time (t90) and injection molding cure times. The correlation is good enough to rank the cure time of various stocks, but not good enough to predict cure times. (4) Injection molded stocks consistently exhibit a lower hardness when compared with stocks compression molded at the same temperature. (5) Injection molded dumbbells produce higher ultimate tensile strength than do die-cut specimens. (6) With few exceptions (i.e., very scorchy stocks), the injection moldability of a stock is not dependent upon the vulcanization system used. (7) Even with NR, rather large variations in injection molding times produce only small changes in initial physical properties. The effects of injection molding and it's variables on compression set, dynamic properties, aging characteristics, fatigue life, and ozone resistance remain unanswered and should be the subject of further evaluations.
Environmental Health Aspects of Carbon Black
Authors: Rivin D. , Smith R. G. 
Published: February 2011

Abstract
Commercial carbon black is a high purity material consisting of more than 99% colloidal carbon. It differs from environmental soots in that the latter are uncontrolled mixtures of various forms of particulate carbon and relatively large amounts of organic tars, resins, and inorganic salts and oxides. Carbon black is considered to be a suspect carcinogen by incorrect analogy with high-extract soot and because it contains polynuclear aromatic hydrocarbons (PAH's), some of which are carcinogens. It is well established, however, that commercial carbon black which has only trace amounts of adsorbed PAH is neither mutagenic nor carcinogenic. Furthermore, carbon black does not cause heart disease or other major illness in animals, except for symptoms associated with lung congestion at dust levels more than tenfold greater than the OSHA PEL of 3.5 mg/ra3. Epidemiologic studies of workers exposed to carbon black dust in North America and Western Europe show no excess in mortality or morbidity due to cancer, heart disease, or respiratory disease. This is generally supported by more limited studies in the USSR and Eastern Europe, except for evidence of respiratory illness in some cases. Due to the absence of adequate control groups and exposure measurements, it is not known whether this apparent health effect results from unusual conditions of occupational exposure—high levels of carbon black and/or other substances—or is due to environmental factors (e.g., cigarette smoking).
Lewis Acid-Base Interactions and Adhesion Theory
Authors: Jensen William B. 
Published: February 2011

Abstract
The above results are intended to be suggestive rather than definitive. Nevertheless, they strongly support the premise that a cross-fertilization of both concepts and experimental data from the apparently unrelated fields of Lewis acid-base chemistry and adhesion theory can lead to potentially valuable results for both fields, emphasizing again the value of using a generalized acid-base vocabulary in describing the phenomena of chemistry, whatever one's area of specialization.
Ridge Formation during the Abrasion of Elastomers
Authors: Bhowmick A. K. 
Published: February 2011

Abstract
Scanning electron microscopy studies have been carried out on gum and filled natural rubber vulcanizates to investigate the ridge formation in the abrasion of elastomers. The first step of the ridge formation is the occurrence of small particles on the smooth abrading surface by a process of microtearing. Their size and shape depend upon the frictional force per unit length of the abrader in contact with the rubber and the nature of the rubber and the abrasive. These particles are not loose, and, hence, are not removed easily if the strength of the matrix is high. Further particles appear on the surface with continued abrasion. These particles coalesce to form fine ridges on the surface which become progressively thicker. Removal of these ridges depends upon the crack growth resistance and strength of the vulcanizate as well as on the dissipation of sliding energy in the matrix. Gum and filled natural rubber vulcanizates follow similar mechanisms of ridge formation. Due to low strength and crack growth resistance of the gum natural rubber, the abrasion resistance is poor compared to the filled ones.
NMR of Reinforced Elastomers: Part II. The Influence of Carbon Black Dispersion
Authors: Wardell G. E. , McBrierty V. J. , Marsland V. 
Published: February 2011

Abstract
1. NMR measurements can provide a fast and efficient monitor of the incorporation and dispersion of carbon black in a reinforced rubber compound. Tests can be carried out at all stages of processing, including masterbatch stock. 2. The technique provides a determination of the fraction of polymer which is bonded to the surface of the carbon black particles. Within a specific formulation, there is reasonably good correlation between the percentage of bonded polymer, determined by NMR, and the degree of dispersion of carbon black determined optically. 3. Bonded polymer formation is sensitive to carbon black type and to the nature of the host elastomer. In comparison of different formulations, there is no correlation between the fraction of bonded polymer and the dispersion of the black. However, carbon black-rubber attachments are fundamental to the phenomenon of reinforcement and, in this respect, NMR bonded-polymer measurements can provide a valuable probe for the investigation of reinforcement. 4. Samples taken from large internal mixers (capacity 200 kg) show that compound inhomogeneity on a gross scale necessitates multiple sampling in order to give an assessment of the average quality of the mix, irrespective of the technique used.