bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress-Strain Behavior of Randomly Crosslinked Polydimethylsiloxane Networks
Authors: Gottlieb M. , Macosko C. W. , Lepsch T. C. 
Published: February 2011

Abstract
We have demonstrated by means of our small-strain data that suppression of junction fluctuations cannot solely account for the discrepancy between experimental modulus values and the predictions of the phantom-network theory. The good agreement between the intercepts in Figures 3 and 4 and the value of GN0 leaves little doubt regarding the relation between the two and the validity of the model represented by Equation (12). Further experiments should be carried out on materials with higher GN0 values than the PDMS chains used here. This will magnify the contribution of trapped entanglements and will demonstrate more clearly the effects discussed here. Further study is also required in order to understand the role played by the polymer backbone on the amount of junction suppression. The question raised by Dossin and Graessley as to whether differences in h values for different networks are due to differences in structure between randomly crosslinked and end-linked networks or to differences in the relative magnitude of topological contributions for different polymers was answered by this work. The agreement of the h value obtained here with those obtained for endlinked PDMS networks indicates that no inherent differences in structure exist between endlinked and crosslinked networks and that differences in polymer backbone are responsible for the values of h obtained. Objections that radiation crosslinked networks are somehow not suitable for testing rubber elasticity theories should also be laid to rest by the good agreement of our results with those of Langley and Polmanteer. The large-strain data obtained here show the ability of Flory's strain energy function to correctly model tension-compression data over the range of crosslink densities covered by this work. Edwards' model did not agree well with our data for low degree of crosslinking samples. Further work is still required since our data exhibited relatively small deviations from Mooney-Rivlin behavior. Finally, the extreme importance of the careful analysis of the materials used, the reaction employed, and the resulting networks was demonstrated. The simplest available method for the verification of the network structure is by the determination of the sol fraction. The extraction of solubles in the case of highly crosslinked networks was found to be susceptible to weighing uncertainty and the presence of unreactive material. The former can be avoided by the use of larger samples, while the latter could be removed by vacuum stripping for our material.
Brass Powder in Rubber Vulcanizates. The Effect on Adhesion
Authors: Parks C. R. 
Published: February 2011

Abstract
Natural rubber vulcanizates loaded with brass powder showed an increase in crosslinking (by swelling measurements), indicating an interaction or bonding between the rubber and brass. Techniques previously employed with reinforcing fillers such as carbon black were used to evaluate the effect of brass on adhesion. The addition of brass powder decreased the scorch time and optimum cure time indicating that the rubber immediately surrounding the brass was being cured at a faster rate. Copper powder, on the other hand, inhibited the cure completely. When exposed to air or oxygen, even small amounts of brass catalyzed oxidation of the rubber.
Compounding Variables Influencing the Reversion Process in Accelerated Curing of Natural Rubber
Authors: Chen C. H. , Collins E. A. , Shelton J. R. , Koenig J. L. 
Published: February 2011

Abstract
Reversion of natural rubber is dependent on the nature of the curing system, choice of accelerator, and the temperature and time of cure. Conventional cure systems which contain a high ratio of sulfur to accelerator have higher moduli at optimum cure, faster rates of cure, but are more vulnerable to reversion. The EV systems, which contain a low ratio of sulfur to accelerator, demonstrate good resistance to reversion but lower moduli at optimum cure and slower rates of cure. The sulfurless cure systems, which represent an extreme case, show greater reversion resistance than EV systems. Of the three accelerators tetramethyl thiuramdisulfide (TMTD), diphenylguanidine (DPG), and N-oxydiethylene benzothiazole-2-sulfenamide (MOR) studied, MOR gives the best performance, followed by DPG, then TMTD in terms of reversion resistance for the cure times studied. In the injection molding of rubber, MOR offers better performance with respect to the requirements of safe scorch times, fast rates of cure, and good reversion resistance. Whenever the conventional cure systems cannot give satisfactory performance, the EV cure system is strongly recommended. If further improvement is needed, such as higher injection and mold temperatures, compensation for the loss of modulus can be made by addition of accelerator and sulfur or simply accelerator alone. Other alternatives are consideration of blends of accelerators as well as blends of natural rubber with other rubbers.
Characterization and Performance of Powdered Rubber
Authors: Burford R. P. , Pittolo M. 
Published: February 2011

Abstract
The performance of rubber crumb in rubber compound and asphalt modification applications depends upon particle size, surface area, and chemical composition. For routine estimation of size and surface area, sophisticated methods including BET nitrogen adsorption and image analysis have limited applicability. The BET technique is capable of further improvement if argon is substituted for nitrogen and degassing of the crumb can be effectively achieved, and if more realistic programs for the estimation of S/V are developed. However, for simple quality control of particle characteristics, low magnification microscopic examination, CTAB titrations, sieve analysis and estimation of bulk density would appear to be adequate. For rubber modification where maximum performance is not required, most crumb can be used at low levels, but fine crumb with high specific surface area is best. For critical applications, extremely fine crumb, or crumb which has undergone chemical modification to improve adhesion or compatibility, would be required, and these steps would lower the economic incentive for recycling. A controlled study of crumb dewetting using individual particles in a model matrix would contribute to an understanding of tensile behavior. For asphalt applications, chemical composition and surface area are more important than particle size in controlling elastic recovery. However, other parameters, including foam development, stability of rubber with time of digestion, and economic factors are also important. Before predictable behavior in asphalt can be achieved, identification and possibly segregation of scrap may be required.
Thermoplastic-Guayule Rubber Blends-Rheological Properties
Authors: Ramos-DeValle L. F. 
Published: February 2011

Abstract
An experimental study of the flow characteristics of blends of natural Guayule rubber with high-density polyethylene was carried out, and the effect of crosslinking and carbon black loading of the rubber phase was examined. It was observed that (1) an increase in shear rate decreases the viscosity and increases the extrudate swell of the blends; (2) an increase in temperature decreases the viscosity of the blends; (3) the viscosity and extrudate swell of the blends appear to be nonadditive functions of the viscosity and extrudate swell of the homopolymers and are lower than predicted by simple additivity; (4) the viscosity increases with increasing degree of crosslinking of the rubber phase; (5) the viscosity increases with increasing carbon black content in the rubber phase, the increase being more pronounced when the rubber-black compound is the continuous phase; (6) when crosslinking was effected, extrudate swell varied in a very peculiar manner, which requires further study. Based on the data presented, it was assumed that in these blends, both components present the same tendency to form the continuous phase at about 60% GR. The formation of a sheath-type configuration, with the component of lower viscosity forming the sheath, was suggested as one of the reasons for the low viscosity of the blends. Finally, it is concluded that as these blends present a relatively low viscosity (the melt flow index at 190°C, with a 5 kg weight, of a 50% GR is about 11 ), they would be suitable for processing in extrusion and/or injection molding. These properties, combined with the mechanical properties mentioned in the accompanying paper, make GR-HDPE blends useful as thermoplastic rubbers and, therefore, offer a promising alternative in the commercialization of natural guayule rubber.
Effect of Reinforcing Silica on Vulcanization, Network Structure, and Technical Properties of Natural Rubber
Authors: Pal P. K. , De S. K. 
Published: February 2011

Abstract
Reinforcement of silica filler in NR in the presence of a silane coupling agent (Si-69), and an additive (TEA) has been analyzed by studies on swelling of the vulcanizate, network structure, technical properties, and scanning electron micrographs. Failure properties in the presence of a coupling agent have been explained on the basis of coupling (polymer-filler) bonds. Improved flex endurance in the presence of TEA has been explained on the basis of good dispersion and better aging resistance of the TEA compounds. Network structure of the rubber during vulcanization undergoes only minor changes on addition of silica filler in the presence of both coupling agent and additive.
Thermal Transition and Relaxation Behavior of Polybutadiene Polyurethanes Based on 2,6-Toluene Diisocyanate
Authors: Brunette C. M. , MacKnight W. J. 
Published: February 2011

Abstract
The thermal transition and relaxation behavior of a series of segmented polyurethanes based on 2,6-toluene diisocyanate-butanediol hard segments and polybutadiene soft segments have been studied via differential scanning calorimetry and rheovibron measurements. Both techniques show a constant low temperature transition at −54°C corresponding to the Tg of the soft butadiene phase and a hard segment transition at about 62°C, both of which are independent of hard segment content. At higher temperatures, a melting endotherm, Tm1, appears between 140 to 150°C followed by recrystallization and then a final melting process, Tm2, between 190 and 210°C. The positions of the melting peaks and the corresponding heats of fusion, ΔHm, show a strong dependence on hard segment content, annealing temperature and, to a lesser degree, on heating rate. The data indicate that crystals of varying stability are formed at different annealing temperatures. Moreover, only those segments involved in the initial crystal distribution (Tm1) which are long enough will give rise to the higher melting crystals, the size and perfection of which are goverened by the hard segment length.
Calculation of Complex Viscosities from Slow-Speed Transient Torque Measurements with the Mooney Rheometer
Authors: Nakajima N. , Harrell E. R. 
Published: February 2011

Abstract
It has been customary to assign certain time scales to given polymer processes. For example, the extrusion process is said to occur at a shear rate in the order of some hundred reciprocal seconds and injection molding at some thousand reciprocal seconds or higher. These statements are usually accompanied by instructions that the viscosity of a material is to be measured at the respective shear rate in order to characterize its processability. However, the above argument is only partially valid, and a single-point viscosity measurement is only a part of the processability evaluation. Inadequacy of the above rationale has been recognized by industry for a long time. With the rapid growth of plastics production in the 1960's, plastic processing went through a technological evolution. In the early stage of evolution of various fabrication techniques, development of suitable grades of material for the respective processes was the major effort of the plastic producers. Soon it became clear that resins which had the same viscosity at the so-called processing shear rate often behaved differently in the actual process. This led to the measurement of the steady-state flow properties at lower shear rates than the so-called processing shear rate, which was representative of the highest shear rate involved in the process. The significant observation was that the viscosity differences of resins often were magnified at the lower shear rate. Sometimes, a subtle difference in processability corresponded to a viscosity difference observable only at very low shear rates. Thus, acquisition of the steady-state flow curve from the low-shear-rate limit (i.e., the Newtonian viscosity) to the high shear rate limit (i.e., the limiting power-law region) became a subject of practical interest. The characterization of such flow curves and their relation to molecular weight distribution (MWD) became a subject of intense study for commercial plastics having a large variation in MWD.
Diffusion of Curatives. I
Authors: Lederer D. A. , Kear K. E. , Kuhls G. H. 
Published: February 2011

Abstract
Curatives will readily migrate across a rubber-to-rubber interface following the classical laws of diffusion. The rate of diffusion increases with increasing temperature. The absolute change in curative concentration diminishes with increasing distance from the interface and increases with time. A test procedure using conventional analytical methods can be used to accurately determine the diffusion coefficients of curatives at various storage temperatures in standard rubber formulations. Diffusion profiles and coefficients are dependent on the curative type. There appears to be a general correlation with molecular weight, with the rate of diffusion decreasing with increasing molecular weight. There is a small, rationalizable effect of concentration on the diffusion coefficient. The diffusion of curatives can cause a significant change in the cure system at or near the interface of a plied rubber article. Diffusion profiles for a particular rubber formulation can be predicted from experimental data using relatively simple analytical and mathematical techniques.
The Scission of Polysulfide Crosslinks in Scrap Rubber Particles through Phase Transfer Catalysis
Authors: Nicholas Paul P. 
Published: February 2011

Abstract
Hydroxide ions transported by onium ions from water into swollen rubber particles rapidly break polysulfide crosslinks with little or no main chain scission. However, methylated monosulfide crosslinks do not cleave under these conditions. The reaction is not truly catalytic because the quaternary ammonium is decomposed. Model studies with N-methyl-N,N,N-tri-n-alkylammonium chlorides and di-2-cyclohexen-1-yl disulfide show that the decomposition reaction involves a highly selective methylation of the thiolate intermediate. However, catalyst decomposition can be inhibited with added alkylating agents. Alkylating agents also improve catalyst efficiency during devulcanization. The Hofmann reaction is yet another route for catalyst decomposition, but the rate is too slow to be competitive. Several onium salts have been examined in this process. In general, those having several large alkyl substituents are the better performers, consistent with the known partitioning/reaction rate behavior of such catalysts in simple, low viscosity solvents. However, with N-methyl-N,N,N-tri-n-alkylammonium chlorides, the rate decreases as the tri-n-alkyl substituents become very large, e.g., C18H37. This may originate from a slow, diffusion-controlled reaction that is peculiar to the network structure of the swollen vulcanizate.
A Laboratory Cutting and Chipping Tester for Evaluating off-the-Road and Heavy-Duty Tire Treads
Authors: Beatty J. R. , Miksch B. J. 
Published: February 2011

Abstract
A laboratory cutting and chipping test for off-the-road, (OTR) and heavy duty, (HD) tires has been developed that predicts service performance with reasonable speed and accuracy. It makes possible the investigation of many compounding factors quickly and inexpensively. A test can be made on a sample in the shape of a disc 5.08 cm diameter by 1.27 cm thickness weighing about 25 g. Test samples can be cured from the mixed rubber compound and the test used for evaluation of either compounding variables or as a tool for quality control. Samples may also be removed from the lugs of vulcanized OTR tires. Cutting and chipping has been defined, and an analysis of the factors thought to be involved in cutting and chipping has been attempted so the necessary criteria for a test could be developed. The resulting apparatus is simple, easily operated, and gives a quick and reproducible test. The test results rate five OTR compounds in order of field experience. Test reproducibility on a single rubber compound of ten test specimens gave values of 1.1 cm ± 0.05 cm, giving a standard deviation of 0.03 or a coefficient of variation of 2.8%. The data discussed show that the necessary physical properties for superior OTR treads are not easily or simply defined. It was found that the reinforcing blacks improve cutting and chipping resistance in approximately the order of their improvement of road test abrasion on a tire. High hysteresis or tan δ is desirable, but must be reduced or compromised for treads of tires where high temperature generation is encountered, such as long, fast hauls with OTR tires.
Response of Carbon Black-in-Oil to Low-Amplitude Dynamic Stress at Audiofrequencies
Authors: Fitzgerald Edwin R. 
Published: February 2011

Abstract
The results reported here demonstrate the feasibility of investigating the dynamic mechanical properties of carbon black-agglomeration networks over wide ranges of temperature and frequency by measurements on carbon black mixed with oil. From the data displayed in Figures 3, 4, 5, and 6, it is evident that the general levels of audiofrequency elastic compliance and modulus, J′ and G′, change more than two orders of magnitude as the temperature is varied between − 12.2 and 50.6°C; the general levels of loss compliance and loss modulus, J″ and G″, change almost as much. A comparison of measurements at 25.2°C made at the beginning and after the conclusion of the measurements at various temperatures (Figure 7) shows little change except for an increase in low frequency values of J″ which are tentatively ascribed to water absorption due to condensation within the sealed measurement apparatus at low temperatures. From this close agreement of before and after compliance values, it is concluded that the large effects of temperature change on the measured dynamic mechanical properties are reversible and essentially independent of thermal history and/or time. The general level of measured dynamic compliance and modulus of the sample of 50 parts by wt. of N299 carbon black in 100 parts by wt. of process oil are also close to those observed for this same carbon black in a cured tire stock for similar temperatures and amounts of black, although the frequency dependences are different. This result agrees with the measurements previously reported by Payne where room temperature values of G′ at 0.1 Hz for carbon black in paraffin oil and for carbon black-butyl rubber were about the same for the same proportion of carbon black. Thus, at low dynamic stress (or strain) amplitudes, the independent carbon-carbon agglomeration network can evidently influence the dynamic mechanical properties of a tire stock as much or more than the cured rubber matrix. The observed broad retardation/relaxation dispersions of compliance and modulus at each temperature clearly cannot be reduced to a common reference temperature by shifts along the frequency axis so that superposition to give composite functions of compliance or modulus over an extended range of frequency is not possible. However, approximate superposition of some compliance and modulus vs. frequency curves to a common reference temperature can be accomplished by vertical shifts indicating that temperature-magnitude reduction may be successful; such reduced curves are shown and treated more extensively in a separate article.
Mixing of Carbon Black with Rubber I. Measurement of Dispersion Rate by Changes in Mixing Torque
Authors: Cotten George R. 
Published: February 2011

Abstract
Analysis of the torque data obtained for a large range of carbon blacks in an oil-extended butadiene rubber (CB-441) shows that the rate of decrease of torque (after the second power peak) follows first order kinetics. The rate of decrease represents the rate of reduction in effective filled volume fraction through dispersion of carbon black agglomerates, and thus, a reduction in the volume of rubber occluded between individual aggregates within the agglomerates. The assumption that the rate of torque reduction is proportional to the rate of carbon black dispersion was tested by examining the responses to various factors influencing the mixing process. In general, the conclusions reached from the analysis of torque data were in agreement with the common industrial experience and predictions based on the mathematical analysis of dispersive mixing. Tadmor's analysis of dispersive mixing predicts that the rate of agglomerate rupture depends on the number of particle-particle contacts and thus is related to the size of individual aggregates, but is independent of agglomerate size. Thus, it is in agreement with the present findings that the rate of dispersive mixing increases with decreasing surface area and increasing structure of aggregates. Increasing polymer-filler interaction gives rise to a faster rate of dispersive mixing, possibly by increasing the effective radii of aggregates through bound rubber formation. Increasing the batch temperature increases the rate of dispersive mixing due to reduced cohesion between the aggregates and a more favorable balance between cohesive and shearing forces. Increasing carbon black loading increases the rate of dispersive mixing by increasing the viscosity and, thus, shearing forces generated during the mixing process. The technique developed in this work may provide a better means for measuring dispersibility of carbon blacks, since other available methods suffer certain disadvantages. For instance, the resistivity measurements are not only dependent on carbon black dispersion, but also on the chemical nature of its surface, while microscopic methods depend on the examination of very small samples that may not be representative of the whole batch.
A Molecular Model of Rubber Elasticity with Contraints on Junctions and Trapped Entanglements
Authors: Queslel J. P. 
Published: February 2011

Abstract
The Flory-Ball model is based on two theories which give a molecular explanation of the origin of junction and trapped entanglement contributions to the modulus exhibited by networks. It also has the advantage that it is valid over the entire range of deformation. It constitutes a proposition which could be the first step of a more general theory. Its experimental verification requires more reliable data.