bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Evaluation of Rubberized Limestone Filler in Asphalt Paving Mixtures
Authors: Bissada Amir F. , Anani Ali A.
Published: February 2011

The method of direct dispersion of small amounts of rubber particles in asphalt binder was associated with difficulties in controlling degradation, mix uniformity, oxidation, and noxious fumes generated by grinding rubber. This study showed that asphalt cements can be modified by adding carboxylated butadiene rubber chemically bound to calcium carbonate to give a wide range of products of different compositions and consistencies. These rubberized fillers can disperse more rapidly in the hot asphalt during the mixing operation and require no adjustments or changes in conventional mixing practices. The conclusions that can be drawn from the experiments conducted include the following: 1. The relatively high stiffening effect of rubberized filler on the F/A binder system is related to its high surface activity or interfacial energy. Limiting values of viscosity increase in F/A binder systems were developed from the effective volume concentration values of rubberized filler to keep resistance to compaction of asphalt paving mixtures within desirable limits. 2. The surface of limestone filler chemically reacted with rubber is rendered more hydrophobic. This results in a pronounced reduction in the stripping of asphalt aggregate surfaces. For uncoated limestone filler, however, the stripping potential increased with the increase of immersion time in water. 3. Temperature susceptibility is decreased by adding rubberized limestone filler to asphalt. 4. Initially, the increase in the RL/L ratio of filler used in the sand-asphalt mixture causes an increase in Marshall stability. After a critical limit (corresponding to the critical effective volume concentration of the fillers in the F/A system), however, the stiffening offers significant resistance to compaction, causing the Marshall stability to decrease. 5. The addition of rubberized filler in RL/L ratios up to 40/60 by weight significantly improved the tensile strength properties of the sand-asphalt mixtures. 6. The values of retained tensile strength after different moisture conditioning methods indicate greater adhesion for mixtures containing rubberized filler up to a RL/L ratio of 40/60 by weight.
Elastomeric Tetramethylene-Ethylethylene-Acrylonitrile Copolymers
Authors: Weinstein A. H.
Published: February 2011

Elastomeric tetramethylene-ethylethylene-acrylonitrile (TEAN) copolymers were prepared by quantitative selective hydrogenation of emulsion NBR polymers in solution in presence of a triphenylphosphine-liganded rhodium salt catalyst. Completeness of hydrogenation at low pressure required appreciable excess of triphenylphosphine. Physical and chemical properties of TEAN gums of varying acrylonitrile segmer content, and their sulfur- and peroxide-cured vulcanizates are characterized. As expected, both gums and vulcanizates were very resistant to attack by oxygen. The exceptionally high tensile strengths of such vulcanizates were attributed to the crystallizability of the gums on stretching. Certain peroxide-cured TEAN vulcanizates prepared from green stocks containing magnesium oxide had a combination of resistance to heat aging in air, hydrogen sulfide, and oil, suggesting their applicability to well-drilling components.
Crosslinking of Halogen-Containing Rubbers with Triazine Dithiols
Authors: Mori Kunio , Nakamura Yoshiro
Published: February 2011

The crosslinking of various halogen-containing rubbers with triazine thiols and metal compounds was investigated, with the following conclusions: (1) Triazine thiols react with halogen-containing rubbers after reacting with metal compounds to form salts. (2) Reactivity of triazine thiols and metal compounds increased with a decrease in thiol pKa, and with an increase in the thiol anion basicity. (3) In this crosslinking, the reactivity of rubbers increased in the order: FR < CPE < PVC < CIP < CO < ECO < CAR < CR. (4) In the crosslinking of CAR, the ether groups in a side chain activated the crosslink site. The sequence of oxyethlene units in ECO was found to activate the crosslinking agents. (5) The active halogen-containing rubbers such as CR and ECO were crosslinked by a combination of inactive F, MgO, and retarders such as Santogard PVI. (6) On the contrary, the crosslinking of rubbers containing inactive halogen, such as soft PVC and FR, was carried out by a combination of active DB, MgO, and accelerators such as polyethylene glycols or onium salts.
Temperature Effects on the Stability of Intermediates and Crosslinks in Sulfur Vulcanization
Authors: Morrison N. J. , Porter M.
Published: February 2011

The dependence of the physical properties of sulfur vulcanizates of diene rubbers on network structure is reviewed and the influence of degree of crosslinking, crosslink structure, and main-chain modification are discussed. In polyisoprenes, these are determined, in practice, by the balance between three competing types of reaction: the conversion of polysulfidic pendent groups into polysulfidic crosslinks; the desulfuration of polysulfidic pendent groups and crosslinks, eventually to the corresponding monosulfides, with recirculation of the removed sulfur into the crosslinking pathway; thermal decomposition of di- and polysulfidic pendent groups and crosslinks with the formation of cyclic sulfide, conjugated diene and triene, and cis, trans-isomerized groups in the rubber chains. At temperatures above about 160°C, the thermal breakdown of monosulfide crosslinks and pendent groups has to be considered. Zinc accelerator-thiolate complexes play a central role in controlling the balance between the various reactions because they promote the primary sulfuration of the rubber to form polysulfidic pendent groups and the conversion of these to crosslinks; they are the agents which desulfurate both pendent groups and crosslinks; they catalyze polysulfide exchange reactions; and in some cases they promote the decomposition of crosslinks. Other factors which affect the balance between these reactions are the temperature and the structure of the main rubber chain in the immediate vicinity of the crosslink. The latter is, in turn, at least partly controlled by the structure and concentration of zinc accelerator-thiolate complexes. The vulcanization of polybutadiene rubbers deviates substantially from this reaction pattern, evidently because the bulk of the accelerator becomes irreversibly bound to the rubber at an early stage. This denudes the vulcanizing system of zinc accelerator-thiolate complexes and, therefore, prevents desulfuration from occurring. The crosslinks thus remain di- and polysulfidic and are apparently less prone to decomposition than in the case of the polyisoprene rubbers, since cyclic sulfides and conjugated hydrocarbon groupings seem not to be prominent products. The removal of accelerator leaves the system unresponsive to zinc and gives it the characteristics of unaccelerated vulcanization with the result that vicinal crosslinking and crosslinks with saturated chain junctions become important products.
Stress Relaxation of NR and NBR: Comparison of Measured Data with Reduced Variables Estimates
Authors: Meier U. , Kuster J. , Mandell J. F.
Published: February 2011

The application of reduced variables has been tested in long-time compressive stress relaxation at 293 K over a time period of 16 years for NR and NBR. The results show that within this time span there is good agreement with predicted data from reduced variables. However, the results indicate that over much longer time periods (approx. 20 to 50 years) disagreement is to be expected due to dominance of chemical stress relaxation for surface to volume ratios in the range of 0.6/mm.
Zinc Oxide Crosslinking Chemistry of Halobutyl Elastomers—A Model Compound Approach
Authors: Vukov R.
Published: February 2011

The study of the crosslinking reactions of halobutyl rubbers with zinc oxide, conducted on low molecular weight model compounds, has brought about a thorough understanding of the chemistry of this process. It has been shown that there are two competitive processes taking place, with the major one generating the catalyst for the oligomerization reaction and producing a substantial amount of a monomeric diene. The actual crosslinking process is a cationically induced oligomerization based on carbon-carbon bond formation. The major high molecular weight product is the dimeric hydrocarbon with a small amount of trimeric product also being formed. Both the direct elimination reaction and the crosslinking process lead to the formation of dienic functional groups.
Plasticization of Nitrile Elastomers by in Situ Grafted Acrylate Monomers
Authors: Eldred Roger J.
Published: February 2011

Grafting of acrylate monomers, such as 2-ethylhexyl acrylate, onto nitrile rubber during the normal cure cycle of the elastomer led to a significant improvement in low-temperature flexibility. This method was shown to provide not only permanent plasticization, but also more than twice the effectiveness obtained by the simple addition of a polymeric acrylic plasticizer. It was found that the improvement in flexibility was directly proportional to the amount of monomer employed. The structure of the monomer was also important in determining its effectiveness, since variations in both the length and chemical composition of the ester side-chain led to changes in the low temperature properties. Improvements were obtained with longer side-chains, while the presence of oxygen in the side chain reduced the effectiveness compared to that of a pure hydrocarbon side-chain. Some slight effect of peroxide type used in the cure system was observed, but no differences in flexibility occurred with variations in cure temperatures between 163° and 204°C.
Acid-Base Contributions to Polymer-Filler Interactions
Authors: Fowkes Frederick M.
Published: February 2011

1. Acid-base interactions determine adsorption and bonding of polymers to fillers. 2. Quantitative predictability of the enthalpy of such bonding is attainable from the Drago C and E equation once the C and E constants are determined for polymers and fillers. 3. Infrared and calorimetric methods are discussed for determining the C and E constants for polymers and fillers. 4. For the case of poly(methylmethacrylate) filled with silica, the enthalpy of bonding has been determined by FTIR spectroscopy. 5. Acid-base interactions between polymers and fillers generate high zeta-potentials which tend to eliminate filler flocculation and reduce viscosity of filled polymer melts.
The Deresination of Guayule: A Physical Model. Part II: A Two-Component Analog for Deresination
Authors: Budiman S. , McIntyre D.
Published: February 2011

Based on GPC, the worm resin can be separated into two distinct groups, large and small. To obtain the overall diffusion coefficients for the two groups that could be useful as commercial design parameters, the worms were converted into wet worm crepe. Diffusion studies with model compounds, abietic acid, and trilinolein, reveal that: (a) their diffusion coefficients for desorption into acetone are inversely proportional to their respective molecular size, (b) the diffusion behavior of the two model compounds in a mixture can be fitted to a simple additive model, and (c) their diffusion coefficients are quite similar to those of the two groups of resin constituents (large and small). It is, therefore, possible to model and optimize a commercial deresination process for guayule worms on the basis of the diffusion behavior of two model compounds linolein and abietic acid and the physical geometry.