bluuebunny/crossref_metadata_2025 huggingface dataset:
Advances in Nitrile Rubber Technology
Authors: Dunn J. R. , Coulthard D. C. , Pfisterer H. A.
Published: February 2011

Considerable advances have been made in NBR technology and still more are possible. The heat resistance of NBR has been raised so that it will with-stand 150°C in air for short periods, instead of 120°C. There is potential in the polymer backbone for still greater stability. It has been demonstrated that the ozone resistance of NBR can be improved by blending with EPDM, but the optimum blend has not yet been developed. The use of PVC to improve the ozone resistance of NBR is now much better understood. Crosslinked NBR has been developed as a non-migratory plasticizer which improves embossing characteristics of PVC and PVC-ABS blends. This, in turn, led to the production of NBR powders which may be used to speed up compounding on conventional equipment and permit rubber to be compounded in equipment generally used for fabricating plastics. Powder black masterbatches of NBR are now being evaluated in industry. Another new product form is liquid NBR, generally with reactive end groups. This is already established as an impact modifier for resins and may be a route to castable reinforced elastomers. Polymer structure modifications such as alternating 50:50 copolymers are interesting but do not appear to have found a market. Carboxylated NBR uses are growing in the wake of improvements in scorch resistance. Reprocessible vulcanizates based on amine-modified NBR have been announced, but a true thermoplastic NBR is still awaited.
Effect of Carbon Black on Dynamic Properties of Rubber Vulcanizates
Authors: Medalia A. I.
Published: February 2011

The term dynamic properties as applied to elastomers refers to the response to periodic or transient forces which do not cause failure or appreciable fatigue (permanent change of properties) during the investigation. Generally this is limited to vulcanizates subjected to deformations not exceeding about 25%; and generally the dynamic properties are measured after several cycles or (in a transient experiment such as resilience) after several preconditioning transients, so that the Mullins effect or difference between first and second strain cycles is not of consequence. Thus, dynamic properties represent the viscoelastic properties of vulcanizates at deformations below about 25%, after reaching a pseudo-equilibrium state. The dynamic properties of rubber are altered tremendously by the addition of a filler. The scope of this article is restricted to the dynamic properties of rubber vulcanizates with carbon black as a filler. The effect covered in this article are important in designing rubber compounds to be used under dynamic conditions, such as tires, power transmission belts, vibration isolation mountings, etc. However, the engineering application of dynamic properties, which has been treated in detail elsewhere, is outside the scope of this review. A certain amount of background material is needed. We will first define the terms used in describing dynamic properties. The methods and instruments used for measuring these properties will be described briefly, and the nature of carbon black will be reviewed. Finally, some historical material is given, together with the dynamic behavior of typical compounds, as a preface to the review of more recent work in this field.
Scrap Tire Disposal Procedures
Authors: Crane G. , Elefritz R. A. , Kay E. L. , Laman J. R.
Published: February 2011

Many procedures and processes for the disposal of scrap tires are available. Because of the complexity of the whole disposal problem—e.g., collection logistics, availability and location of markets for products generated from scrap tires, as well as economics—no one procedure or process is believed to be sufficiently outstanding that all scrap tires would be so processed. Several procedures or processes must be used to solve this industry problem. The procedure or process selected for disposing of scrap tires will be dictated primarily by economics and geographic location. Certainly, all procedures must be proven environmentally acceptable.
13C NMR Characterization of Polychloroprene Microstructure II. Relaxation, NOE, and Quantitative Measurements
Authors: Coleman M. M. , Brame E. G.
Published: February 2011

Spin relaxation, NOE, and quantitative measurements have been performed on chloroprene polymers prepared by free radical techniques in the range −150 to +90°C. 13C NMR has proved to be an excellent method for the characterization of polychloroprene microstructure. From our quantitative results it would appear that the concentration of cis-1,4 structural irregularities has been considerably overestimated in previous infrared studies. In addition, the relative amount of trans-1,4 inversions (HT) appears to be somewhat higher than previously reported.
Unsolved Problems in Polymer Degradation
Authors: Dunn J. R.
Published: February 2011

This review has highlighted some of the major problems in polymer degradation. It will be apparent that the degradation of commercial rubbers and plastics is exceedingly complex, since processing and small quantities of impurities or additives can interact and totally change the behavior of the substrate. It is not sufficient to examine the degradation of pure materials. The pure polymer may be studied as a base line but in order to obtain the full story it must also be studied in presence of known impurities or additives added singly and also in combination. This systematic approach is laborious and seldom used. The need for more realistic tests is now being recognized. Outdoor exposure combines the effects of uv light, heat, rain, ozone, nitrogen dioxide, and sulfur dioxide. A laboratory test should take all such elements into account. If a part is to be exposed to oil and air in the presence of heat, as it may be in an automobile, laboratory tests must examine the combined effects of these. The literature contains a wealth of information on the degradation of model compounds and pure materials, and copious empirical information on the behavior of commercial materials. The explanation of what happens in practice and, especially, the production of commercial polymers which give close to ideal behavior, is much more elusive.
Effect of Elevated Temperature on the Unaccelerated and Accelerated Sulfur Vulcanization of Natural Rubber
Authors: Mukhopadhyay R. , De S. K.
Published: February 2011

High cure temperature up to 180°C seems to have no significant effect on the mechanism of unaccelerated sulfur vulcanization of natural rubber. In the case of accelerated systems, the conventional ones undergo more desulfurization and decomposition of the initially formed polysulfidic crosslinks at higher cure temperature. The EV systems show less dependence on cure temperature, and the main maturing reaction seems to be desulfurization of the polysulfidic crosslinks. The semi-EV system shows behavior intermediate between the conventional system and the EV one. Expectedly, the EV systems show better resistance to reversion at high cure temperature than the conventional and semi-EV systems.
Molding of Rubber
Authors: Sommer J. G.
Published: February 2011

The purpose of this paper is to survey the materials, methods, problems and special treatments associated with molding rubber. Rubbers with quite different rheological behavior are readily molded using various methods such as compression and injection for millable compositions, while the more recent reaction injection molding (RIM) method is used for molding low-viscosity polyurethanes. A comparison of RIM with the more established methods shows advantages for RIM, especially for high modulus compositions. Molding problems such as porosity, shrinkage and mold fouling are briefly reviewed along with means of alleviating these problems. A number of molding variables and their associated ranges are considered. The ranges vary significantly. The weight range of molded parts varies by about ten decades, while the range of thermal diffusivities for different rubbers and compositions is less than one decade. The ratio for in-mold times for different materials and methods is intermediate, varying by three decades. Both pretreatments and posttreatments are associated with molding rubber. For example, preheating off-the-road tires before molding compensates for low thermal diffusivity. Posttreatments permit modifying surface friction, altering and stabilizing dimensions, improving flammability characteristics and other properties.
Influence of Carbon Black on Processability of Rubber Stocks III. Extensional Viscosity
Authors: Cotten G. R. , Thiele J. L.
Published: February 2011

A new instrument for measurement of extensional viscosity was designed and employed in the evaluation of SBR compounds containing carbon black and other non-black fillers. It was shown that carbon black filled rubbers generally do not reach steady-state viscosity ; the stress continues to increase with increasing strain up to the point of rupture, due to rapid orientation of molecular chains during extensional flow. The data was evaluated in terms of the Denn-Marrucci equation, and the effect of carbon black on the two adjustable parameters was found. It was found that higher carbon black loading or structure increases only the viscosity coefficient, i.e., it changes the relative level of the flow curve without changing its shape. On the other hand, an increase in surface area increases both the viscosity coefficient and the relaxation time, i.e., it increases the upward curvature of the flow curve. A very good correlation was observed between Mooney viscosity values and calculated viscosity coefficients. Some agreement was found between calculated relaxation times and the rates of stress relaxation for rubbers containing nonblack fillers, while in carbon black loaded stocks the observed differences in stress relaxation rates were too small to draw definite conclusions. The use of high surface area, low structure carbon black is recommended for applications where stiffening of the SBR compounds during extension is desired.
Measurement of Carbon Black Dispersion in Rubber by Surface Analysis
Authors: Vegvari P. C. , Hess W. M. , Chirico V. E.
Published: February 2011

A stylus-type surface roughness tester has been applied to the study of carbon black dispersion in a number of different rubber systems. The method is based on a freshly cut rubber surface which is tracked by the stylus to provide a roughness trace on a strip chart. Carbon black agglomerates deflect the cut path because of their higher hardness relative to the surrounding matrix. Thus, surface roughness diminishes at increasing levels of dispersion. A quantitative index of dispersion quality may be derived from the frequency and average height of the roughness peaks. The method offers a distinct advantage over previous methods in its ability to provide precise dispersion ratings over a very wide range of rubber processing levels from the masterbatch to the final product. The technique is applicable to the analysis of unvulcanized rubber compounds and could be utilized as a factory quality control procedure. Direct interfacing of the surface analyzer to a programmable calculator would provide quantitative dispersion ratings within five minutes of the receipt of a sample. Studies of varied carbon black dispersions in SBR and SBR/BR passenger tread formulations have confirmed the work of previous authors. Tensile strength, fatigue life, resilience, elongation, and extrusion shrinkage increased at higher dispersion levels, while Mooney viscosity, Shore hardness and heat buildup exhibited a progressive decrease. The properties of a 50/50 NR/BR truck tread formulation showed a more varied response to black dispersion. Tensile strength and resilience showed considerably less dispersion dependence than SBR and SBR/BR. However, the tensile response increases with increasing black fineness and decreasing structure, while resilience showed the opposite trend. Fatigue life and heat buildup showed the same trends observed for SBR and SBR/BR. However, NR/BR treadwear (radial tires) showed considerably less dependence on dispersion above the 70% level, in comparison to those other polymers (bias ply tires). NR/BR with N220 at a dispersion index of 68 gave treadwear resistance that was equivalent to the same compound at a dispersion index of 89. However, dispersion indices of 50 or lower caused severely depressed treadwear resistance for the different blacks that were tested. The milling of NR/BR masterbatches cooled overnight produced significantly higher dispersion levels in comparison to hot batches at the same total mixing energy. This procedure can be employed to optimize treadwear and other properties at lower levels of energy consumption.
Injection Molding of Rubber
Authors: Wheelans M. A.
Published: February 2011

The outline of a strategy for the injection molding of a safe mix is described. Safe accelerators, safe curing systems, and mixes are suggested with machine conditions which should yield short curing times for a wide range of products. Comparisons have been made of the vulcanizate properties of injection and compression moldings prepared from the same mix in the same mold and press at the same temperature. Results have shown that, although anisotropy is more pronounced in injection moldings, the mean of values for modulus along and at 90° to radial mold flow lines of an optimum modulus cure are the same (within experimental error) as the mean of values for modulus along and at 90° to mill flow lines in a compression molding also cured to its optimum modulus. Injection moldings are similar to compression moldings in volume swelling and hardness but they have marginally higher rebound resilience and marginally lower compression set. The effect of an increase in mold temperature is to give a valuable reduction in cure time, but it also causes a reduction in modulus and modulus dependent vulcanizate properties. Optimum values for maximum-minimum Monsanto Rheometer torque, relaxed modulus, and 300% modulus are reduced to 77– 79% of their optimum values at 160°C when cured at 200°C, but this reduction can be compensated for by adding higher levels of accelerator or accelerator and sulphur. Although a certain degree of anisotropy may have to be tolerated, the analysis of vulcanizate properties has provided a means of understanding and correcting an injection molding mix which fails to pass a specification. It gives confidence that NR can be cured at relatively high temperatures such as 180–190°C, which make injection molding profitable.
Effect of Composition on Shrinkage of Mold Cured Elastomeric Compounds
Authors: Beatty J. R.
Published: February 2011

The mold shrinkage of elastomer compositions depends upon the elastomer employed, the volume percent of elastomer plus all other organic materials, and the kind and amount of pigment present. The specific effects of pigments in inhibiting the shrinkage are shown. A procedure is given by which the shrinkage of most soft rubber compositions of the common elastomers may be calculated from the recipe. The major part of the shrinkage of elastomer compositions is due to the much greater thermal contraction of the composition than that of the mold. This portion of the shrinkage depends upon the thermal coefficient of expansion of the composition and mold and the temperature difference between the curing and room temperatures. A minor part of the shrinkage is due to a contraction in volume resulting from vulcanization. For normal soft rubber stocks with sulfur concentrations of three phr or less and for normal neoprene stocks, this factor may be neglected. For stocks having higher sulfur ratios an allowance needs to be made for this factor. Shrinkage of fiber loaded stocks should be determined carefully depending on the quantity, and particularly on the degree of orientation of the processed stock.
Application of Pulsed NMR to Elastomeric Composite Systems
Authors: Nishi T.
Published: February 2011

As has been shown, pulsed NMR can be applied to elastomeric composites in various ways. Other possible applications are to the study of crosslinking of elastomers; the effect of plasticizer, tackifier, or processing oil on elastomers; structure-property relationships for block copolymers (including polyurethane); liquid elastomers; thermoplastic elastomers, etc.; crystallization of elastomers under normal conditions or under extension. The advantages of pulsed NMR are that it is not affected by the physical state of the sample, the ease of temperature variation, and the short time required for data acquisition. However, it is necessary to choose the proper technique to analyse the system, and careful consideration must be taken of the effect of spin diffusion (for T1 measurement) and system recovery time, after a giant pulse for the measurement of free induction decay.
Cohesive Strength in Guayule Rubber and Its Improvement through Chemical Promotion
Authors: de Valle L. F. Ramos , Montelongo M.
Published: February 2011

Green (cohesive) strength of Guayule rubber (GR) was determined and compared to that of natural rubber (NR). In the case of GR gum compounds the green strength was shown to be inferior to that of NR gum compounds; however, in the case of black compounds GR green strength was similar to that of NR. Green strength was very much improved in both rubbers by the addition of MNNA (N-(2-methyl-2-nitropropyl)-4-nitroso aniline) for gum and black compounds. MNNA also acted as an accelerator and thus reduced the difference in vulcanization rate between NR and GR. When using MNNA, a reduction in energy consumption during mastication was also noted. Finally, MNNA notably increased the tensile modulus and decreased the elongation at break for GR vulcanizates, while maintaining an almost constant tensile strength.
Coupling Agents for Certain Types of Fluoroelastomers
Authors: Martin J. W. , Braswell T. V. , Green H. E.
Published: February 2011

From the data presented in this paper, it is concluded that fillers can be coupled with certain types of fluoroelastomer base polymers. A useful coupling agent must have mechanical and thermal properties at least equivalent to the base polymer in order to provide an improvement in properties for the compound under extreme service conditions. For the particular case of peroxide-curable fluoroelastomers and carbon fillers, hydroxy-terminated low-molecular-weight polybutadienes with high 1,2-microstructure appear to be good coupling agents. Care must be exercised in selecting the peroxide level to obtain a high crosslink density of the coupling agent while retaining rubberlike properties of the compound. This type of polybutadienediol has a relatively high number of reactive vinyl groups (approximately 20 per molecule) and relatively high molecular weight. Based upon the hypotheses presented in this paper, that coupling between carbon black and fluoroelastomers has been demonstrated for the first time, both higher molecular weight and multifunctionality of the polybutadienediol are viewed as important characteristics for effective performance.
Monitoring the Molding Process
Authors: Hindmarch R. S.
Published: February 2011

The monitoring of the molding process should be taken on as wide a scale as possible with a greater emphasis on the early stages of the process, incoming polymer and ingredients, mixing, blending, and cure studies, to reduce the need for very critical monitoring at the molding stage. Monitoring at a late stage in any process should not be aimed at identifying batch-to-batch variation, which has often been the case, but at achieving greater throughput of good product by optimizing the process and identifying machine faults.
Smoke Properties of Highly Filled Ethylene-Propylene-Diene Terpolymer Rubbers
Authors: Mosesman M. , Ingham J. D.
Published: February 2011

The observations made in this work indicate the difficulty in extracting generalizations about how efficiently hydrates serve to control smoke levels in a fire situation which involves periods of pyrolysis and of combustion. In our opinion magnesium hydroxide deserves serious consideration as a smoke retardant for EPDM rubbers. This is based on its superior performance in the flaming smoke test, its moderately good performance in the early part of nonfiaming smoke test, its high LOI, and its reinforcing properties. The electrical properties of the Mg(OH)2 filled EPDM rubber indicate that it could be acceptable for some types of electrical insulation or cable covering applications.
Degradative Effects of Guayule Resin on Natural Rubber
Authors: Keller R. W. , Winkler D. S. , Stephens H. L.
Published: February 2011

This study indicates that the degradative effects of guayule resin on natural rubber are due to the presence of unsaturated fatty acids in the resin. Since linoleic acid is, by far, the most abundant unsaturated fatty acid in guayule resin, it appears that linoleic acid is primarily responsible for the degradative effects of guayule resin on natural rubber. A possible mechanism to explain the acceleration of natural rubber degradation caused by linoleic acid can be developed by fitting linoleic acid into the Bolland oxidation mechanism for hydrocarbon polymers.
Adsorption of Sodium Dodecyl Sulfate on Natural Rubber Latex Particles and Determination of Specific Surface Area of the Particles
Authors: Chen S. F.
Published: February 2011

Soap titration of polymer latex is a widely used method for the determination of the specific surface area and particle size in synthetic latices. The method involves the titration of a latex of known polymer and soap content with a standard soap solution until the critical micelle concentration (CMC) is reached. At this concentration, saturation adsorption of the soap to form a monolayer on the particle surface occurs. From a knowledge of the amount and kind of soap adsorbed and the effective molecular area of the soap on the surface, the specific surface area and average diameter of the particles can be calculated. The effective molecular area of soap at saturation adsorption on polymer particle surface has been determined by comparing adsorption data with particle size data obtained by electron microscopy. Little information is available on the adsorption of sodium dodecyl sulfate (SDS) on NR latex particles. In ammoniated latex, these particles are covered by a complex mixture of proteins, fatty acid soaps, and lipids, the composition and concentration of which are not known accurately. Cockbain modified the soap titration method of determining particle sizes in synthetic latices and claimed that it was applicable to NR latices. In this method SDS was titrated to the latex adjusted to pH 6 ± 0.2. It was assumed that at this pH the interfacial activity of SDS was high while that of the proteins and fatty acid soaps initially present on the latex particles was comparatively low. Under these conditions the SDS would displace almost all the proteins and fatty acid soaps on the particles when sufficient SDS has been added to form micelles in the aqueous phase. The specific surface area was calculated from the SDS adsorption after assuming the molecular adsorption area of SDS to be 60 A˚. No account was taken of the effect of the poly(vinyl alcohol) creaming agent on adsorption. Sekhar found that Cockbain's method of soap titration was temperature dependent. Van den Tempel has shown that electron microscopy cannot yield accurate specific surface area of NR latex particles because of the heterogeneous particle size distribution inherent in unconcentrated latex.
Temperature Effect of Electrical Resistivity of Carbon Black Filled Polymers
Authors: Voet Andries
Published: February 2011

Very large positive temperature coefficients of resistivity (PTC) found in a narrow temperature range with dispersions of carbon blacks in noncrystallizing polymers are caused by an increase in average particle or aggregate distances of the dispersed black. This effect is the result of their deagglomeration upon temperature increase, induced by the increased Brownian motion, predominantly caused by the large reduction in vehicle viscosity and aided by the increase in segmental motion of the polymeric molecules. Highest PTC effects are found in the range of the steepest resistivity-concentration curves for the carbon black dispersion, differing markedly for each black and each polymer. The range itself is determined by particle size, density, degree of aggregation and agglomeration, and by the presence of surface oxides. In crystalline polymers high PTC effects are predominantly caused by the large volume expansion of the polymer in the melting range, as well as by the formation of a uniform melt from a two phase system of amorphous and crystalline components. Carbon black particles are mostly restricted to the amorphous phase in the solid, but are able to disperse into the entire volume of the melt. The effects of crosslinking the polymer as well as the influence of strain on PTC effects are considered. The decline in PTC effects above the peak temperature is discussed.
Role of Adhesion in Viscoelastic Properties of Rubber-Tire Cord Composites
Authors: Prevorsek D. C. , Sharma R. K.
Published: February 2011

Dynamic mechanical measurements have been carried out on samples of rubber and PET cord-rubber composites, with and without adhesive, as a function of strain amplitude, temperature, pretension, angle of strain application and time of cycling. The results show that mechanical loss and dynamic modulus depend on these variables as well as the presence and type of adhesive at the cord-rubber interface. Based on these results, we conclude that adhesion plays a significant role in the viscoelastic properties of a composite and it is an important factor along with the properties of components in the analysis of tire performance in terms of composite properties. This study clearly shows that the maximum adhesion may not be the optimum adhesion in tire technology. The most relevant question, i.e., the determination of the optimum level of adhesion for a specific tire, however, remains unanswered. The viscoelastic properties of the composites decrease with time of cycling but the rate of decrease depends upon the level of adhesion in the starting material. This result could be important in the development of a more realistic dynamic adhesion test. Attempts to use the viscoelastic experiments with small amplitude, high frequency strain to determine the onset of fracture in the composite specimen appears to be promising. Work is in progress to determine the potential of this method in the analysis of adhesion.
Mixing Process of Natural and Synthetic Polyisoprene Rubbers
Authors: Ponce M. A. , Ramirez R. R.
Published: February 2011

The mixing process, in a Brabender Plasticorder with a cam-type mixing head, was studied with NR (natural Hevea rubber), GR (natural guayule rubber) and IR (synthetic polyisoprene) at two different temperatures (60 and 80°C), with three types of carbon black (EPC, FEF and HAF), each one at three different concentrations (30, 50 and 70 phr). Samples for analysis were obtained at six different mixing times. Development of mixing and dispersion was evaluated through the black incorporation times (BIT), energy consumption, and tensile properties, which have been correlated to the degree of dispersion determined by low resolution microscopy. BIT, Optimum Mixing Times and the energy consumed to reach those points are lower for GR and IR than for NR. Compounds obtained at Optimum Mixing Times show that GR has a lower modulus, similar tensile strength and higher elongations.
Model Networks of End-Linked Polydimethylsiloxane Chains. X. Bimodal Networks Prepared in Two-Stage Reactions Designed to Give High Spatial Heterogeneity
Authors: Mark J. E. , Andrady A. L.
Published: February 2011

End-linking mixtures of very short and relatively long polydimethylsiloxane chains with a multi-functional alkoxy silane yields model elastomeric networks having a bimodal chain length distributions, and earlier studies have shown that this compositional heterogeneity increases the ultimate properties of the networks. The present investigation focuses on possible additional effects of the spatial heterogeneity introduced by the prereaction of some of the very short chains into tightly crosslinked domains. Increasing the extent of prereaction did not give any significant increases in modulus or ultimate strength. Thus, it is indicated that the unusual ultimate properties of bimodal networks are due to limited chain extensibilities, rather than to reinforcing effects.
Tack and Green Strength of Elastomeric Materials
Authors: Hamed G. R.
Published: February 2011

Tack and green strength are two important properties of many elastomer compounds. Tack is the ability of two materials to resist separation after bringing their surfaces into contact for a short time under a light pressure. Two types can be defined: autohesive tack (autohesion), where both materials have the same chemical composition and adhesive tack, in which the two materials have dissimilar compositions. The green strength of an elastomer is its resistance to deformation and fracture before vulcanization. Rubber stocks that are used in tire manufacture (or other plied-up operations) must have a certain minimum level of tack and green strength. Tack is necessary so that the many components of a green tire will hold together until molding. This requires not only that the components exhibit quick stick when building, but also that the tack bonds have long term creep resistance, since the green tire may be hung on a rack several days before molding and vulcanization. In addition, an uncured tire must have good green strength so that it will not creep and hence distort excessively before molding or tear during the expansion that occurs upon molding (or in the second stage for a radial tire). Adhesive tack is an important property of pressure sensitive tapes. Although some of the basic criterion necessary to obtain high autohesive tack or high adhesive tack are similar, this review will focus primarily on autohesion. Thus, unless otherwise staled, the term “tack” will refer to autohesive tack. However, ideas and results will be presented from the literature on pressure sensitive adhesives when such information leads to a further understanding of autohesion.
Probing Macromolecular Motions through Viscoelasticity
Authors: Ferry John D.
Published: February 2011

My personal random walk has included numerous other steps, including branches as well as closed loops that returned unproductively to square one. However, this is enough for the present occasion. I close with deep gratitude to the more than fifty graduate students and more than thirty postdoctorate and other associates with whom I have had the good fortune to collaborate over the years. Obviously, most of the work I have described is theirs, and I represent them in receiving the Medal. I apologize that only a few of their names have been mentioned here. I also thank the University of Wisconsin for providing an environment so favorable to research and scholarship and for supporting our work in many ways, direct and indirect. Finally, we have had financial support from numerous government agencies and several industrial firms, all acknowledged with gratitude. Once again, I deeply appreciate the honor I have received here and the privilege of speaking to you today.
Vulcanization of Butyl Rubber: Curative Effects of 2-Pentadecylbenzoquinonedioxime
Authors: Ghatge N. D. , Maldar N. N.
Published: February 2011

The structure-property relationships of butyl rubber vulcanizates derived from quinonedioxime-red lead or quinonedioxime-MBTS-sulfur cure systems were studied. The effects of the dioxime curatives on the mechanical properties of the elastomer are discussed on the basis of rheological and heat-aging study. It was found that a 2-pentadecylbenzoquinonedioxime-MBTS-sulfur cured butyl rubber vulcanizate shows good retention of tensile strength on heat aging at 125°C.
A Novel Optical Method for Estimating the Dispersion of Carbon Black in Rubbers
Authors: Ebell P. C. , Hemsley D. A.
Published: February 2011

The work reported is part of a large program aimed at examining the internal mixing of rubbers and its effect on properties. The dispersion of carbon black in the compound is of primary importance. Standard microscopical methods used industrially to measure this parameter are either subjective or lack discrimination at the higher levels of dispersion. To study mixing behavior effectively it is necessary to be able to assess the property over a wide range of degrees of dispersion. A technique based on the analysis of the dark field image produced by a reflected light microscope has been developed. The specimen preparation is simple, and analysis is carried out using a standard T.V. system. The technique gives results which are sufficiently discriminating to allow correlation of black dispersion with processing and mechanical properties, even at extremely high levels of mixing. An additional advantage of the method is that unvulcanized samples may be used.
Response of Carbon Black Filled Butyl Rubber to Cyclic Loading
Authors: Mckenna G. B. , Zapas L. J.
Published: February 2011

The stress softening behavior of a carbon black filled butyl rubber in cyclic loading (creep) and cyclic deformation (stress relaxation) histories was investigated. Single step and multiple step stress relaxation and creep experiments were conducted as were creep experiments with sinusoidal loading histories. The data were analyzed in view of the BKZ constitutive equation. For materials which follow the behavior predicted by the BKZ theory, the single step stress relaxation response is a lower bound for the stress in cyclic deformation histories, and the single step creep response is an upper bound for the deformations obtained in cyclic loading histories. In our experiments we observed that for filled butyl rubber, the responses to cyclic deformation and cyclic loading histories were outside these bounds. The softening was much more emphatic in cyclic loading histories than in cyclic deformation histories. We also found that the rubber is stiffer in creep than predicted from the BKZ theory (from stress relaxation data). It is suggested that an adequate description of material behavior might be obtained using a theory similar to the BKZ theory, which includes competing effects of stiffening in creep and softening under load-unload cycling. The failure lifetime of the filled butyl rubber in cyclic loading histories was related to the stress softening behavior. If it is assumed that, in some sense, a failure envelope exists, then it can be shown that under cyclic loading the filled butyl rubber should fail at a time earlier than under constant load conditions. We were able to predict failure lifetimes by using creep data obtained from short time cyclic loading histories and extrapolating to the strain at break determined from a shifted failure envelope. This approach relates the observed frequency and waveform dependence of failure lifetimes to the creep behavior under cyclic loading conditions.
Model Elastomeric Networks
Authors: Mark J. E.
Published: February 2011

Tetrafunctional and trifunctional model polymer networks of known crosslink density were prepared by end-linking a variety of hydroxyl terminated chains both in the undiluted state and in solution. The polymers employed were poly(dimethylsiloxane), atactic poly(propylene oxide), poly(ethylene oxide), poly(tetramethylene oxide), and poly(e-caprolactone), and the end-linking agents were alkoxy silanes and an aromatic triisocyanate. The resulting networks were studied (i) in elongation at 25°C, both in the unswollen state and swollen with a nonvolatile diluent, and (ii) in equilibrium swelling in benzene. The values of the elongation modulus in the limits at large and small deformations were found to be in good agreement with recent theoretical predictions for nonaffine and affine deformations, respectively (the latter corresponding to the case in which the displacements of the network chain vectors are a simple linear function of the macroscopic strain). Comparisons between the tetrafunctional and trifunctional siloxane networks showed that both of these moduli have very nearly the expected dependence on network functionality. The swelling equilibrium results were found to be in very good agreement with a recent theory of network swelling in which the closeness of the approach to the affine limit depends on both the network structure and the degree of swelling. None of the results provided evidence for very significant contributions from interchain entanglements. Several of the polymers, however, have large values of the "plateau modulus" in the uncrosslinked state, and are therefore generally considered to have high densities of entanglements of this type. The present results thus contradict the widely held notion that interchain entanglements should contribute to equilibrium elastomeric properties to nearly the same extent as they do to the dynamic, visco-elastic properties.
Rubber-Thermoplastic Compositions. Part IV. Thermoplastic Vulcanizates from Various Rubber-Plastic Combinations
Authors: Coran A. Y. , Patel R.
Published: February 2011

The ultimate mechanical properties (σB and εB) and elastic recovery (inversely measured by tension set) of dynamically vulcanized melt mixed rubber-plastic blends increase with the similarity of the rubber and plastic in respect to the critical surface tension for melting γc. They also increase with the crystallinity Wc of the plastic (resin) phase. Stiffness, as measured by Young's modulus E, increases with the differences in surface energy between the two phases.
Microdomain Structure and Some Related Properties of Block Copolymers. II. Plastic Deformation Mechanisms of the Glassy Component in Rubber-Toughened Plastics
Authors: Kawai Hiromichi , Hashimoto Takeji , Miyoshi Katsunori , Uno Hiroyuki , Fujimura Mineo
Published: February 2011

The toughening mechanism was investigated by means of mechanical and optical techniques including electron microscopy and polarized light scattering for wide variety of domain morphologies of di- and triblock copolymers and their blends with corresponding homopolymers. Two types of plastic deformation mechanisms of the glassy component are emphasized as the toughening mechanism. One is large plastic deformation of the glassy component, as bulk, followed by its plastic flow or fragmentation, depending on the di- or triblock sequence arrangement. The other is the development of a microcraze at the boundary of the rubber particle, and its propagation through the glassy matrix. The origins of the two types of plastic deformation mechanisms are postulated as hydrostatic pressure effects upon the high plasticity of the glassy component due to differences of Poisson's ratios between the glassy and rubbery components and also as stress concentration effects of the rubber particle at the glassy phase opposite to the equatorial zone of the rubber particle with respect to the principal stress direction. The nearer the volume fraction of the two components to 50/50, the more efficient are the hydrostatic pressure effects upon inducing high plasticity in the glassy component. On the other hand, the smaller the radius of curvature at the equatorial zone of the rubber particle, the more concentrated the stress level becomes to generate the microcraze and further microcracks. Thus, there must be an optimum size of the rubber particle to generate the microcrazes in the most efficient rate. The system of alternating lamellar microdomains is sufficient for the generation of high plasticity, but insufficient for the craze development due to a too large radius of curvature to elevate the concentrated stress, if any. The toughening mechanism in rubber-toughened plastics can be explained generally in terms of these counter-balanced factors for the two types of plastic deformation mechanisms of the glassy component.
Interfacial Considerations in Polysulfide Sealant Bonding
Authors: Usmani A. M. , Chartoff R. P. , Warner W. M. , Butler J. M. , Salyer I. O. , Miller D. E.
Published: February 2011

It is necessary to examine the sealant-coating interface and consider the polymer-primer interaction for a complete understanding of interfacial bonding. Why a polysulfide sealant sticks to a fresh or “imaged” polyurethane coating surface and not to an “aged” polyurethane surface has been determined. Also, we were able to artificially age polyurethane coated surfaces and correlate artificial aging with natural aging by surface tension and contact angle measurements. The polyurethane kinetic studies indicate that unreacted isocyanate (NCO) groups at the surface quickly deplete in a matter of few hours under 60°C/95 percent R.H. condition. Both heat and moisture reduce the NCO concentration in bulk but at a moderately slower rate. Room temperature cure of the polyurethane was found to be very slow. Disappearance of residual NCO groups during aging coupled with hardening of the polyurethane surface appears to be the primary reason for inadequate adhesion with a polysulfide sealant to an aged polyurethane coating. Titanate primer reacts with polysulfide resin to give chemically bonded product, whereas no reaction with “aged” and “unaged” polyurethane coated surfaces was detected. The strong solvency of the primer, however, softens and lowers the glass transition temperature (Tg) of the polyurethane coating. Insofar as the polysulfide adhesion improvement onto “aged” polyurethane surface is concerned, we found that an alkyl phosphatotitanate and mercaptofunctional silane are effective adhesion promoters, whereas oxirane-functional silane and a polymeric isocyanate are ineffective primers. The SEM study of sealant-coating interface revealed that water is one of the most potent desorbing agents. The SEM method is quite valuable and should therefore be further refined. The adhesion of polysulfide sealant to new polyurethane surface can be attributed to the reaction of residual NCO groups with the polysulfide to form polythiourethane that resist desorption by JRF and moisture. Since “aged” polyurethane surfaces contain too few residual NCO groups, the resultant adhesion of the polysulfide sealant is poor. The use of a titanate primer, however, produces adequate adhesion. The titanate interacts with the polysulfide but does not react with the polyurethane surface. The titanate and solvent combination, however, interfaces with the polyurethane surface by softening it and producing microroughness and thereby increasing mechanical interlocking. Another reason the primer functions is by removing or lifting a monomolecular (or thicker) water layer from the polyurethane surface and allowing the sealant to “wet” or get “closer” to polyurethane. Incorporation of epoxy modification in a polysulfide sealant improves adhesion to “aged” polyurethane surface because epoxy groups can react with urethane groups. Additionally, hydroxyl and nitrogen groups may produce increased attractive forces.
Rubber-Thermoplastic Compositions. Part V. Selecting Polymers for Thermoplastic Vulcanizates
Authors: Coran A. Y. , Patel R. P. , Williams D.
Published: February 2011

Based on a few characteristics of the pure rubber and plastic components, rubber-plastic combinations can be selected, with a high probability of success, to give thermoplastic vulcanizates (by dynamic vulcanization) of good mechanical integrity and elastic recovery. The characteristics used in the selection are estimated surface energies, crystallinity of the hard phase (plastic) material and the critical chain length, of the rubber molecules, for entanglement. The best compositions are prepared when the surface energies of the rubber and plastic material are matched, when the entanglement molecular length of the rubber is low (high entanglement density) and when the plastic material is crystalline. Of course, it is required that neither the plastic, nor the rubber decompose in the presence of the other at temperatures required for melt mixing. Also, a curing system is required, appropriate for the rubber under the conditions of melt-mixing.
Glass Transition Behavior of Polyisoprene: The Influence of Molecular Weight, Terminal Hydroxy Groups, Microstructure, and Chain Branching
Authors: Kow C. , Morton M. , Fetters L. J. , Hadjichristidis N.
Published: February 2011

The glass transition temperatures for a series of high-1,4 linear and star-branched polyisoprenes have been measured by differential scanning calorimetry. The Fox-Flory relation for the linear polyisoprenes was found to be Tg=Tg∞−1.76×104Mn−1. The influence of hydroxyl groups on Tg was also examined for low molecular weight (<2.2×104) polyisoprenes.
Chemical and Scanning Electron Microscopy Studies on Fatigue Failure of Natural Rubber Vulcanizates
Authors: Mathew N. M. , Bhowmick A. K. , De S. K.
Published: February 2011

Gum and filled vulcanizates with both conventional and EV systems were tested in a De Mattia flexing machine at two temperatures, and the fracture surfaces were subjected to chemical analyses and SEM studies. The study shows that flexing failure is not accompanied by any major change in network structure. SEM studies show ductile failure of gum mixes. HAF black filled mixes show brittle failure which changes to quasi-ductile with the addition of antioxidant. At 100°C, flow of the matrix is more predominant.
One-Component Heat Curable Urethane Liquid Elastomers
Authors: O'Connor J. M. , Sessions W. J. , Lickei D. L.
Published: February 2011

Quite clearly this study does not fully achieve the objectives stated earlier. The data show that fairly good quality storage stable one-component elastomers may be produced from acrylic modified urethane oligomers thermally cured with polyfunctional mercaptans and peroxide. Unfortunately, some of the advantages of a liquid system are lost because a reinforcing filler must be added in order to achieve acceptable physical properties. At the levels studied in this design, the filler and % hard segment play only a minor role in influencing the physical properties of the system. Those oligomers with low average functionality and low unsaturation appear to give the best physical properties, and further improvements may be achieved by looking at higher molecular weight polyols which, for a given functionality, will produce oligomers with lower unsaturation. Clearly, our screening study was not extensive enough to fully elucidate the utility of this concept. In order to determine what order of properties may be achievable by this approach, it will be necessary to design experiments that consider the effects of the other variables not evaluated in our initial study. For instance, we held the mercaptan constant throughout this work. It is trifunctional and was used at a 10% excess. Beneficial effects may be achieved with less than an excess or a greater excess or by evaluating mercaptans with reduced or elevated functionality. The cure conditions should be optimized and the effect of conventional rubber accelerators or additives screened. The oligomer for the most part consists of a polyol. We chose to evaluate only the 1500 equivalent weight polyether polyols for most of our preparations. We indicated earlier that it may be beneficial to look at higher equivalent weight polyols in order to minimize the unsaturation for a given functionality. Also, urethanes derived from polyester polyols generally possess superior physical properties compared to those based on polyethers, and it may be worthwhile to examine polyester polyol based oligomers. Carbon black, as well as fully adequate mixing, should be looked at to completely define the process.
Short Jute Fiber Reinforced Rubber Composites
Authors: Murty V. M. , De S. K.
Published: February 2011

The following conclusions can be drawn from the above results and discussion: (1) The bonding between jute fiber and rubber matrix is poor without any bonding agent. (2) Addition of 5 phr silica is essential and sufficient for promoting adhesion between fiber and matrix of a mix containing 5 phr resorcinol and 3.2 phr (3) The jute fiber will act as a reinforcing filler only when added above a volume loading of 10 percent. (4) The aging resistance of jute fiber reinforced natural rubber composites is excellent beyond a fiber loading of 10 volume percent.