bluuebunny/crossref_metadata_2025 huggingface dataset:
Tack and Green Strength of NR, SBR and NR/SBR Blends
Authors: Hamed G. R.
Published: February 2011

1. A simple NR compound has superior tack compared to an SBR stock because of its greater ability to flow under compressive load and its higher green strength. The difference becomes greater as surface roughness is increased or test rate decreased. Tack differences between the two stocks can be quantitatively explained without assuming differences in the interdiffusion rate of SBR and NR molecules. NR is an “ideal” material for developing high tack. It can be processed to a low viscosity and still maintain high green strength. Furthermore, the mechanism responsible for the high green strength (strain crystallization) is not active in the bond formation step, hence does not interfere with contact and interdiffusion, but rather develops upon stressing. SBR, on the other hand, depends on entanglements, which tend to inhibit flow, to achieve green strength. Thus, if the molecular weight of the SBR is raised to enhance green strength to the level of NR, the stock will flow very poorly. Likewise, if SBR molecular weight is lowered, flow can be improved substantially, but green strength will decrease rapidly. Either of the above conditions result in poor tack. 2. For smooth, shiny surfaces brought together, contact occurs rapidly and nearly completely for both the NR and SBR stocks. This results in a relative tack near unity and hence, in this case, the tack strength is really a measure of stock green strength, i.e., tack is green strength limited. Obviously, when this condition exists, the addition to the stock of plasticizers, tackifiers, oils or other additives to facilitate stock flow (but decrease green strength) will nontheless reduce tack. Here, tack can only be increased by enhancing stock green strength, preferable without hindering flow ability. 3. The relative tack of SBR and SBR-dominated blends with moderately rough surfaces is less than unity and increases with contact pressure. Thus, tack is contact limited. In this instance, relative tack can be improved by decreasing stock viscosity, however, absolute tack will only be increased if good green strength is maintained. This may be the mechanism for the action of commencal tackifiers. 4. The tack of NR/SBR blends passes through a maximum with composition at about 80% NR. This is readily understood by noting that the green strength also reaches a maximum at this composition. For NR/SBR blends containing 60% or more of NR, green strength plays the dominant role in controlling tack. 5. Uncured adhesion of SBR to NR is less than the tack of either pure component. This suggests that interdiffusion is required to obtain high tack.
Effects of Wax and Substituted p-Phenylenediamine Antiozonants in Rubber
Authors: Lederer D. A. , Fath M. A.
Published: February 2011

Wax was found to reduce fatigue life and dynamic ozone resistance. These losses can be partially compensated for by the addition of a substituted paraphenylenediamine (PPD). An increase in PPD concentration leads to a slight increase in wax bloom. At low levels of wax (1 phr), this effect will lead to a significant increase in static ozone protection. A critical level of wax bloom is required to form a continuous film for optimum static ozone protection. The relative increase in ozone protection provided by a wax/PPD combination was similar for both an NR tread and an NR/BR sidewall formulation. The amount of wax bloom was much higher in the NR/BR compound compared to the NR stock. In both cases, however, the critical level of wax bloom was exceeded; thus, a significant difference in static ozone protection is not expected. At practical levels of antiozonant, no synergism between wax and PPD was observed in static or dynamic ozone exposure tests. Significant synergism was observed under intermittent test conditions. This is due to a combination of the effective static ozone protection of the wax with the dynamic protection of the PPD.
Effects of Carbon Black Types on Treadwear of Radial and Bias Tires at Variable Test Severities
Authors: Wilder C. R. , Haws J. R. , Cooper W. T.
Published: February 2011

Trends observed in testing various types of carbon blacks in radial tires follow those observed in bias tires with some differences, as noted in the following statements. There is less advantage for the use of high structure blacks in radial tires than found in bias tires. The improvement of wear resistance with blacks of increased surface area in radial tires is equal to or greater than that found in bias tires. Good dispersion of carbon black is important for good treadwear in all tires, but adverse effects of poor dispersion appear reduced in radial tires.
Laboratory Simulation of a Factory Extrusion Process by the Die Swell Tester
Authors: Tokita Noboru
Published: February 2011

The simulation principle (scaling) of the tire tubing process was studied by the “Die Swell Tester”. It was found that once the following three conditions were established, the die swells (ratio of extrudate to die cross section) of factory tubed extrudate were identical to lab scale DS results: namely, (1) same operation temperature, (2) same residence time in die, and (3) same ratio of die length to die diameter (L/D). In order to obtain the same L/D values between the complicated die shape of a factory tuber and the circular die of the DST, it is shown that the hydraulic radii (area/perimeters) must be kept the same. The correlation coefficient between factory extrudate properties and DST values was 99.6%. On the contrary, the Mooney torque ML1 + 4 values did not correlate with the die swell properties of the factory extrudates. Cold shrinkage of cut lengths of factory extrudates was simulated by the use of an extension control attachment to the DST. The theoretical analysis of potential recovery was established using die swell values and the stretch ratios. A good correlation between potential recovery (or total stretch) and cold shrinkage was obtained in both factory and laboratory samples.
Mold-Flow-Induced Anisotropy in Nitrile Rubber
Authors: Chang W. V. , Yang P. H. , Salovey R.
Published: February 2011

1. Data in all the investigated locations showed anisotropic swelling. The anisotropy is believed to be induced by vulcanization of the rubber in a strained state caused by mold flow. 2. Data and theories of composite networks suggest that the swelling of rubber in the strained direction would be less than in other directions. 3. Anisotropic swelling data were consistent with the flow pattern of rubber in the mold. 4. The volumetric swell ratios at different locations varied only slightly, in-dicating that crosslinking was uniform. 5. The shear rate for compression molding is 1–10 s−1, calendering is 10–102 s−1 extrusion is 102–103 s−1, and injection molding is 103–104 s−1. Hence, rubber products processed by other methods are expected to be even more anisotropic. 6. Microswelling is a fast and easy technique to monitor the strain-induced anisotropy and to infer the flow pattern during mold filling. 7. Mechanical data of composite networks formed under different strains should be collected, and theories should be checked, then, mechanical behavior of networks based on microswelling data may be predictable. 8. Engineering design for both end use and molding should take this frozen strain-induced anisotropy into consideration.
Processability Testing
Authors: Norman R. H. , Johnson P. S.
Published: February 2011

There should be no need for processability testing. If one controls adequately all the raw materials and all the processes prior to the tests, then the resultant materials will all have predictable processability. In the real world, one can try, but never achieve, this state of perfection, so that some processability testing may be essential for process control purposes. The progression from (a) dumping a mixed batch at constant cycle time to (b) dumping at a fixed temperature to (c) dumping at a fixed unit work shows a progressive attempt to produce a more consistent material in spite of the imperfections of the raw material and the process. No one processability tester is adequate for all purposes. The choice of processability testers for process control depends upon the polymer and the subsequent process to which the material or mix is to be subjected. Factors which can be significant are times, shear rates, temperatures, and whether the test modifies the relevant properties. Most of the published information relating to process control relates to controlled experiments rather than to processing under normal factory conditions. However, it is probable that much information on factory experience remains unpublished in order to avoid disclosure of commercially valuable information or, on the other hand, to avoid admission of mixing failures. The cost of purchasing and running the processability testing equipment has to be balanced against the costs of not recognizing a bad batch and the cost of delaying further processing while the tests are made. For these reasons no general recommendation can be made except that a single piece of data is insufficient to characterize either a polymer or a mix. Any factory will probably need several types of processability testing if it wants more than a very cursory view of the material being processed. The choice of a processability test for development of mix composition depends upon the degree of information which it is economical to acquire. If an order calls for an isolated 400 kg of material for a noncritical application, it may be worth doing no processability testing at all. On the other hand, if a factory is to produce hundreds of tonnes per week of a single type of mix, it is well worth while discovering considerable detail about the characteristics of that mix. In this case, equipment providing fundamental data over a wide range of shear rates and at small and large strains may avoid carrying processes so near to a critical condition that any slight change in material or process may cause a catastrophe. Many factory activities fall between these examples and thus require individual consideration.
Recent Advances in Gel Permeation Chromatography
Authors: Ouano A. C.
Published: February 2011

Gel permeation chromatography (GPC), sometimes referred to as size-exclusion chromatography (SEC), has progressed at an almost explosive rate since its introduction less than two decades ago. One has only to refer to the open literature or thumb through the list of Chromatographic equipment manufacturers anxious to sell their latest innovation to be fully convinced of this fact. Because of the extensive progress in GPC technique and instrumentation, the author had a very difficult time in deciding the scope of this review. Mindful that he may be criticized of being myopic in his presentation of the most significant and recent contributions and guilty of gross omission of important references, the author has nevertheless decided to narrow the scope to three major areas and a few key references. The three major areas to be covered are: (1) data acquisition and processing, (2) high-pressure chromatography and (3) detectors. Extensive progress has been made in the computerization of both data acquisition and data reduction, the latter allowing molecular weight distribution (MWD) and molecular weight averages to be obtained on the sample in a matter of minutes rather than hours or days. The main beneficiaries of the computerization of data acquisition and processing have been those concerned with polymer quality control, for it has liberated them from the drudgery of the manual digitization, integration, and normalization of the chromatograms required to reduce them to a useful format. The hours of monotonous eye-straining work to obtain MWD and molecular weight averages has been reduced to a few seconds of punching a few keys of the data system console. The development of the high-pressure Chromatograph has added a new dimension to GPC, for, when it is combined with a computerized data system, the MWD can be obtained almost in real time in relation, for example, to a characteristic time of a polymerization reactor. In high-speed Chromatograph y under nearly ideal conditions (low-viscosity mobile phase and molecular weight of no more than a few hundred thousand), the MWD can be obtained in a few minutes. This capability allows the use of GPC as on-line process-control equipment. The Chromatograph can be used as part of a “feed-back” loop to control the polymerization conditions to obtain a product of consistent MWD.
Recent Advances in Anionic Polymerization
Authors: Halasa Adel F.
Published: February 2011

In summary, one can say that the versatility of living polymerization makes it a very useful and unique technique. Synthetic polymer chemists can utilize the lithium at the end of the chain to add polymer-like conjugated monomers, in order to tailor-make the polymer chain, or they can use chelating diamines to change the microstructure of the polymer chain. They can also run hydrogenation on anionically prepared polydienes to produce thermoplastic elastomers. They can transform anionically made polymer chain ends by adding ethylene oxide, carbon dioxide and halogens. This paper has emphasized recent advances in this field.
Time Dependent Nonlinear Viscoelastic Behavior of Polymer Fluids—A Review of Current Understanding
Authors: Soong David S.
Published: February 2011

The behavior of concentrated polymer solutions and melts in transient flows has been under active investigation in recent years. This research interest stems from the realization that a better understanding of these time dependent phenomena has the potential to greatly improve existing industrial processes and to provide new insights to polymer dynamics. In this article, various aspects of the transient viscoelastic properties are discussed. Special emphases are placed on some important considerations in acquiring reliable transient data. Several promising network theories capable of interpreting these experimental results are reviewed. Future research challenges, such as the design of more complicated and stringent rheological tests for the established models, have also been identified.
Guayule
Authors: Eagle F. A.
Published: February 2011

The microstructure of both GR and NR is comprised of cis-polyisoprene units, resulting in a physicochemical similarity between the two rubbers. However, the processing and vulcanizate properties of guayule and NR differ when the former is substituted in standard NR formulations. Since GR and NR do not contain the same nonrubber constituents, equivalent compounding and processing may not work equally well on both. Therefore, guayule's formulations must be modified in order to use its properties to best advantage. This has recently been demonstrated using standard production equipment and modified NR formulations, with very little disruption to the manufacturing process. It can therefore be concluded that guayule is a useful substitute for NR, and once it is commercially available, applications will be readily found.
Elastomeric Diene/Polyhalophenyl Acrylic Copolymers with Intrinsic Flame Retardance
Authors: Weinstein A. H.
Published: February 2011

It is well known that certain aliphatic or aromatic halogen-containing substituents impart flame retardance to compounds containing them. This fact has been applied not only to development of fire retardant additives for organic compositions but also to preparation of various halogen-containing polymers with intrinsic fire retardance. These include resinous or fibrous homopolymers or copolymers of polyhalophenyl methacrylates or acrylates. The monomers used for these contain relatively high concentrations of highly heat stable aromatic halogen groups and may be prepared by various means from available, potentially low-cost polyhalophenols. The present report describes efforts to prepare elastomeric diene-copolymers with intrinsic flame retardance by the use of such monomers. Utilization of these monomers for the preparation of elastomeric terpolymers with fairly good low-temperature properties and oil resistance is also illustrated.
Vulcanization and Vulcanizate Properties of a Fluoroelastomer Containing Epoxy Groups as Cure Sites
Authors: Kojima G. , Kojima H. , Morozumi M. , Wachi H. , Hlsasue M.
Published: February 2011

The vulcanization behavior and vulcanizate properties of tetrafluoroethylene-propylene elastomer containing a small amount of glycidyl vinyl ether as cure site was investigated both at room temperature and at high temperature with different types of the vulcanizing agents. The conclusions are: 1. Glycidyl vinyl ether incorporates into the tetrafluoroethylene-propylene copolymerization system without disturbing the alternating microstructure and works as an efficient cure site. 2. The room-temperature vulcanization of the terpolymer proceeds at an adequate rate when tris(dimethylaminomethyl)phenol is used as the curative together with phenol as the accelerating agent. 3. Coatings of the terpolymer make a tough finish on many substrates such as steel and hydrocarbon rubbers and protect the substrates from hostile environments. 4. The vulcanization behavior of the terpolymer at high temperature is much influenced by the kind of curative. The carboxylate of hexamethylenediamine [e.g., hexamethylenediamine-N,N′-bis(p-isopropylbenzoate)] provides balanced vulcanization behavior and mechanical properties suitable for molding articles of complex shapes. 5. The mechanical and chemical properties of the high-temperature vulcanizate thus obtained are similar to those of the tetrafluoroethylene-propylene binary system vulcanized by peroxide.
Influence of Large Static Deformation on the Dynamic Properties of Polymers Part II. Influence of Carbon Black Loading
Authors: Meinecke E. A. , Maksin S.
Published: February 2011

The influence of carbon black loading on the dynamic properties of statically deformed elastomers has been investigated. The energy loss per cycle was found to increase according to the square of the strain amplification factor as expressed by the Guth-Gold-Einstein equation. The dynamic complex modulus |E*| is approximately equal to the static modulus obtained from the slope of the static stress-strain curve. The influence of carbon black loading on E* can, therefore, be predicted from its influence on the static stress-strain curve which was found to be governed by the first power of the strain amplification factor. The tangent of the loss angle can thus be predicted from |E*| and the energy loss per cycle. It does not only depend upon the dynamic viscosity of the material; it also depends upon the shape of the stress-strain curve as well.
Study of Transport Phenomena in Guayule Deresination
Authors: Budiman S. , McIntyre D.
Published: February 2011

Renewed interest in guayule as an alternative source of natural rubber has brought the processing aspect back into focus as an important determinant in the effort of guayule commercialization. To meet the current technological requirement, the quality of the guayule rubber needs to be standardized like the presently known Technically Specified Natural Rubber. In order to produce good standard quality guayule rubber, the resin constituent must be thoroughly and consistently eliminated. This condition stipulates an effective and efficient extraction process which in consequence demands a thorough understanding of the resin compounds and their behavior during extraction with acetone. The emphasis of this study is to examine the physical state of resin inclusion in the rubber and the mechanism of its removal during solvent extraction. The ultimate objective is to determine the necessary transport parameters in the deresination process of guayule latex coagulum, better known as ‘worms’ in popular terminology. Worm deresination was used in guayule processing in the U. S. during World War II, and it is currently also performed in the CIQA Pilot Plant in Saltillo, Mexico. Previous work on the subject had been carried out by Banigan and Clark of the U. S. Natural Rubber Research Station at Salinas, California in the early 1950's. Banigan had determined that the worm deresination occurred by diffusion and made experiments to determine diffusion coefficients using thin sheets of dried worms with acetone, ethanol and methylethyl ketone as solvents. He also noted the possibility of two different diffusion coefficients due to the mixed nature of guayule resin. Recent investigations at CIQA have confirmed that the resin consists of two major groups, namely the nonvolatiles and the volatiles. The nonvolatile components are mainly fatty acid triglycerides, while the volatiles are terpenoids such as α-pinene, dipentene, etc. The present study attempts to provide more detailed transport data using modem analytical techniques and the current knowledge of transport processes in polymeric materials. Since the available diffusion data are only for dried worms, whereas in reality the worms are deresinated in the wet state, the present work has used wet worms as the study material.
Transport Methods of Determining Particle Size Distributions in Colloidal Systems
Authors: Shuster C. D. , Schroeder J. R. , McIntyre D.
Published: February 2011

The two techniques examined in this work yield information about the particle size distribution of the latexes studied. The ease of measurement is improved over previous methods used on broadly distributed latexes. The TPC curves for both the natural and synthetic latexes correlate with the centrifuge curves. Both techniques show the Hevea to have larger particles than the guayule. The techniques also show SBR latex samples 1 and 2 to have larger particles than samples 3 and 4. The TPC is useful only for particles between 0.3 µm and 20 µm in size. The centrifuge can be used for any size range of particles by altering the rotor speed or eluant density. By employing the proper mathematics, these data could be easily converted from optical density distributions to particle size distributions.
Shearography: A New Optical Method for Nondestructive Evaluation of Tires
Authors: Hung Y. Y. , Grant R. M.
Published: February 2011

Shearography, a new means of nondestructive testing, has been presented. This paper merely gives some preliminary exploration of shearography for non-destructive testing of tires. Nondestructive testing by shearography is based on the comparison of two states of strain in tires. Ideally, it is desirable to impose stresses similar to those found in service and in an actual malfunction. Therefore, methods of stressing more realistic than the present method of stressing by partial vacuum should be explored. It is believed that only the surface of the potential of shearography has been scratched. In fact, shearography can be used to evaluate the integrity of virtually any structural components, built of any materials—plastics, rubber, metals, composite materials, etc. The full capability of shearography still awaits to be explored.
Gelation and Fusion Characteristics of PVC Resins in Plastisols by Determination of Their Viscoelasticity
Authors: Nakajima N. , Ward D. W.
Published: February 2011

A poly(vinyl chloride) (PVC) plastisol is a suspension of fine particles of PVC dispersion resin in a plasticizer. The particle size ranges typically from about 15 to 0.2 µm and smaller. The PVC particles in the plastisol consist of the primary particles, which are products of polymerization, and of the agglomerates of the primary particles, which result from the spray drying and subsequent grinding. The commercial applications of plastisols are coatings, films, sheets, foams and rotational castings, where the plastisol is first spread on substrates, and then heated to gel and fuse. PVC dispersion resins are used to produce a variety of formulations, including those for automotive applications, coated fabrics and resilient flooring. Requirements for the plastisols are many; for example, good air release, viscosity stability, fine particle size, foamability and good heat stability. In general, the processability requirements emphasize the rheological behavior at room temperature and the gelation-fusion behavior, the latter being the subject of this paper. When a PVC plastisol is heated, the resin particles are penetrated by the plasticizer and become swollen. Consequently, the system becomes a dry, coherent mass; at this point the material has not attained its ultimate strength. This stage is called gelation. Upon continued heating to a higher temperature (e.g., 195°C) the microcrystallites of PVC melt and the polymer molecules fuse together more uniformly. Upon cooling, the material exhibits the intrinsic strength of a plasticized PVC. The rates of gelation and fusion are important and are often critical aspects of the processing of the plastisol. For example, the rate of gelation controls the residence time needed to build the wall thickness desired in slush molded boots or hot dip molded pieces. Gel rate also affects the uniformity of rotocast parts and the penetration of plastisol into fabric in cast coating operations. Fusion rate and the rate of decrease in melt viscosity after fusion affect uniformity of cells in chemically blown foams. Therefore, many commercial grades of PVC dispersion resins are offered, each having a different rate of gelation, fusion and ultimate properties.
Ambient Temperature Effects on Tire Rolling Loss
Authors: Schuring D. J. , Hall G. L.
Published: February 2011

The temperature of the ambient air surrounding an operating tire is an important component of the complex thermal system producing rolling loss. Rolling loss is defined as the amount of heat generated by the rolling tire per unit distance. Figure 1 indicates that part of this heat is conducted and stored within the tire body, part is dissipated at the tire surface. The dissipated heat is directly affected by the temperature of the ambient air. Since all heat modes are interactive, the ambient air temperature must therefore influence the heat generated by the tire and, hence, its rolling loss. Presently, relations between ambient air temperature and rolling loss can be established only through measurements; mathematical models of tire heat generation and distribution have not reached a stage where they can be easily applied.
Water-Resistant Release Coating for Uncured Rubber
Authors: Kuan T. H. , Sommer J. G.
Published: February 2011

Rubber is conventionally formed into sheets or slabs on a two-roll mill. These are immersed in a release agent (slab dip), followed by cooling and drying in air. The low rate of cooling associated with air limits the throughput in rubber mixers. The throughput can be significantly increased through the use of water for cooling. However, water cannot be used with conventional slab dips; it washes them from the rubber slabs, causing the slabs to stick together after stacking. A new slab dip now permits cooling rubber slabs rapidly with water. After they are dried and stacked, the slabs do not stick together. The new dip contains a unique combination of a carboxylated SBR latex, a heat sensitizer, fillers and other additives. The heat sensitizer causes the latex to gel rapidly after it contacts the hot surface of the rubber slabs; this provides a water-resistant release coating. Other additives in this slab dip control its wetting and rheological behavior. The new dip does not significantly alter physical properties of rubber compounds after they are coated and reprocessed.
Thioketals as Prevulcanization Inhibitors
Authors: Morita E. , Sullivan A. B.
Published: February 2011

Thioketals prepared from active methylene compounds are introduced as a new class of nonthioimide prevulcanization inhibitors and compared to other inhibitors in various accelerator systems. The chemical nature of the inhibition by these thioketals has been examined from the interrelations of chemical structure of the thioketals, 13C chemical shift of the quaternary carbon, rate of reaction with 2-mercaptobenzothiazole, and scorch delay.
Factors Affecting the Extrudate Swell and Melt Fracture Phenomena of Rubber Compounds
Authors: Leblanc Jean L.
Published: February 2011

Post-extrusion swelling and extrudate distortion phenomena reveal the viscoelastic nature of elastomeric materials and are particularly critical in rubber processing. With the short dies used in the rubber industry, it is clear that extrudate swell depends not only on the rheological properties of the compounds, but also on the particular geometry of the extrusion system. Consequently, it is very difficult to compare laboratory results with the experience of industrial practice, because of the number and variety of extrusion processes. However, it is possible to draw some generally valid conclusions from the data currently available. The main factors affecting post-extrusion swelling and the critical conditions for the onset of extrudate distortion are: (1) the elastomer, its nature and molecular characteristics; (2) the filler, its grade and level; (3) the (cumulative) energy introduced into the rubber during the mixing operations; (4) the mixing procedure (particularly in blend preparation); (5) the temperature and shear conditions of the extrusion process. The use of sophisticated test instruments, such as the MPT enables the processability parameters of a compound to be rapidly obtained, which can often be used as a key to solve practical plant problems.
Room-Temperature-Cured Polydimethylsiloxane Elastomers from Aqueous Dispersion
Authors: Saam J. C. , Graiver D. , Baile M.
Published: February 2011

The observations are consistent with the formation of grafts of hydrophilic silicates to the silanol chain ends at the surface of the PDMS emulsion particles prior to removal of the water. The silicates may be introduced into the system directly or through the alkaline colloidal silica, which contains appreciable amounts of dissolved silicates. Monomeric, or possibly dimeric, silicate grafted to more than one chain end could migrate to the interior of the PDMS emulsion particle to form further crosslinks. Grafts to higher molecular weight silicates and silicate grafts bearing anionic charge would be solvated with water and tend to remain at the oil-water interface. This could provide steric as well as ionic stabilization to the PDMS particles, and the system would no longer respond to electrolytes as a simple, ionically stabilized, hydrophobic colloid but more as a hydrophilic colloid resembling silica. The role of the dioctyltin dilaurate is to interact in the water phase with the water-soluble silicates to render them, in effect, hydrophobic and to transport them to the oil-water interface. There the dialkyltin species can catalyze condensation between silanol on the silicate with silanol on the PDMS chain ends. Alkyltin acylates are known to hydrolyze in aqueous alkaline media, and the product can condense with silanol on the silicate to form silastannoxane intermediates. These are relatively stable to hydrolysis, provided bulky groups are present on tin as in dioctyltin dilaurate.
An Overview: New Ideas in Nondestructive Evaluation
Authors: Berger Harold
Published: February 2011

It is recognized that present methods for NDE of tires emphasize x-radiography, ultrasonics, and holographic interferometry. Modifications of these approaches in terms of improved signal processing, image magnification (for x rays), electronic focus (for ultrasonics), and tomographic imaging appear to offer promise for improved NDE of tires. In addition, techniques such as acoustic emission, pulsed eddy currents, microwaves, and vibrothermography also show promise. The suggestion that other NDE methods now being investigated for application to composite structures be followed closely appears valid as does the concept of improved procedures to verify the condition of raw materials used in initial fabrication.
The Influence of Carbon Black on the Reversion Process in Sulfur-Accelerated Vulcanization of Natural Rubber
Authors: Chen C. H. , Koenig J. L. , Shelton J. R. , Collins E. A.
Published: February 2011

The effect of carbon black upon the reversion process in the sulfur-accelerated vulcanization of natural rubber has been studied. It is found that black-filled cure systems have a faster rate of vulcanization and better reversion resistance. The net decrease of trans-methine content, which is equivalent to the improvement of reversion resistance, is found to be at most 15%, with the initial 10 pphr loading yielding the greatest effect. However, those decreases of trans-methine content are small when compared with the substantial effects of these fillers on the physical-mechanical properties of the vulcanizate, which is a linear function of black loading. In general, the smaller the black particle size, the greater the improvement of the reversion resistance, but particle size alone is not the only factor affecting reversion. A universal curve is obtained for correlating the amount of reversion and trans-methine content, which is independent of any natural rubber-based curing system, operating conditions and type of fillers.
Degradative Studies Related to the Plasticity Retention Index of the Standard Malasian Rubber Scheme. I. Kinetics of Degradation
Authors: Sambhi Manjit S.
Published: February 2011

Molecular degradation is the main process occurring during the high temperature oxidative aging of most commercial grades of natural rubber. The degradation as measured in terms of Wallace plasticities exhibit first-order kinetics for about 50% extent of degradation. PRI can now be expressed in terms of the first-order rate constant of degradation and is independent of the initial plasticity of the rubber. The observed first-order behavior has been explained in terms of linear intrinsic viscosities versus Wallace plasticities. PRI can be interpreted in terms of the molecular chain length. Complications can, however, arise if hardening of the rubber can occur concurrently with degradation during the PRI test. We then obtain inflated PRI values which overestimate the abilities of the rubbers to resist molecular breakdown, if PRI is considered to arise from degradation only. Perhaps, in order to nullify any possible hardening contribution to PRI values, the PRI test could be designed for rubbers which have undergone some form of controlled accelerated storage-hardening in a manner that prohibits oxidative degradation.
Formation and Structure of End-Linked Elastomer Networks
Authors: Dušek Karel
Published: February 2011

The network structure of end-linked polymer networks prepared from telechelic polymers is determined mainly by the functionality distribution of the telechelic polymer, the relative reactivity of the functional groups, and the conditions of network formation. The main feature of network formation by end-linking (by a step reaction) is a relatively high critical conversion at the gel point and a relatively narrow range of conversions available for the build-up of the network structure. Therefore, the final equilibrium properties (modulus and degree of swelling) are rather sensitive to cyclization, incompleteness of the reaction, and possible errors in the determination of the content of functional groups or functionality. The wastage of bonds in elastically inactive cycles is rather low, amounting to several per cent, but its effect on the concentration of EANC's is not negligible. In multicomponent systems, where two or more structurally differing components contain groups of the same kind, chemical clustering (e.g., formation of hard clusters) occurs and affects the concentration of EANC's as well as a number of physical properties. For polyurethane networks, mechanical, dielectric and optical measurements indicate that networks of poly(oxypropylene)triol and diisocyanate are more homogeneous than those of poly(oxypropylene)diols, 1,1,1-trimethylolpropane, and diisocyanate, and that the two-stage process yields more homogeneous networks than the one-stage one. The correlations between the concentration of EANC's and the gel fraction can be generalized and employed in examining the rubber elasticity theories or the degree of crosslinking of industrially important elastomer networks. In addition to the common features, the endlinking processes have their own specificities given by differences in the crosslinking mechanisms and, sometimes, in physical interactions. An example of a more complex network formation (and a correspondingly more difficult theoretical treatment) is crosslinking of carboxyl-terminated rubbers with diepoxides.
Scanning Electron Microscopy Studies of Tear of Carboxylated Nitrile Rubber
Authors: Chakraborty S. K. , Bhowmick A. K. , De S. K. , Dhindaw B. K.
Published: February 2011

Mechanism of tear of unfilled and carbon black filled carboxylated nitrile rubber (XNBR) having metallocarboxylate crosslinks, sulfur-sulfur crosslinks and mixed type crosslinking systems has been studied by Scanning Electron Microscope. Tear proceeds through stick-slip process in the case of gum mixes. The number of tear lines is more in the sulfur crosslinked system, resulting in poor tear strength. Addition of reinforcing carbon black changes the mechanism of tear. The sulfur crosslinked system shows knotty tear, while introduction of ionic crosslinks results in smooth tear presumably due to the large tip diameter reaching the edge of the specimen.
A Direct Experimental Determination of the Elastic Contribution of Chain Entangling in a Tightly Crosslinked Elastomer
Authors: Batsberg W. , Kramer O.
Published: February 2011

The experimental result, that the equilibrium force is nearly equal to the pseudoequilibrium force immediately prior to quenching and irradiation, allows the following conclusions: (1) Chain scission during crosslinking is not a serious problem. (2) The network of highly entangled linear chains is effectively at elastic equilibrium immediately prior to crosslinking in the strained state. This would not be the case if the entangled structure remained untrapped. (3) The effect of chain entangling in tightly crosslinked elastomers is large, also at elastic equilibrium. In fact, it is almost quantitatively equal to the pseudo-equilibrium stress relaxation modulus of the uncrosslinked linear polymer. This result is in agreement with the results from the Langley and the two-network methods.
Measurement of Tensile Strength of Natural Rubber Vulcanizates at Elevated Temperature
Authors: Bell C. L. M. , Stinson D. , Thomas A. G.
Published: February 2011

The tensile strength of test pieces made from natural rubber vulcanizates drops abruptly at a critical temperature which can vary from 40 to 130°C. This variation in critical temperature is shown here to be a result of the variation in critical cut length with temperature. When the naturally occurring flaws in the test piece are smaller than the critical cut length, high tensile strength values occur, but when the flaws are longer than the critical cut length, low tensile strength values occur. The critical cut length decreases as the temperature increases, and the abrupt drop in tensile strength occurs as the critical cut length reaches the natural flaw size in the test piece. The natural flaw size in tensile test pieces depends on the sharpness of the cutter, and for tensile strength measurements at elevated temperature, it is shown that even a slightly blunt cutter may give markedly different results from a sharp one.
Polytetramethylene Ether Glycol: Effect of Concentration, Molecular Weight, and Molecular Weight Distribution on Properties of MDI/BDO-Based Polyurethanes
Authors: Pechhold E. , Pruckmayr G.
Published: February 2011

Hardness, modulus, and tear strength of PTMEG-based polyurethanes are mainly affected by the hard-segment (MDI/BDO) concentration. On the other hand, PTMEG molecular weight mainly influences low-temperature and dynamic properties. Resilience and hydrolytic stability are affected by both soft-segment concentration and chain length. PTMEG of narrow molecular weight distribution yields softer polyurethanes with considerably longer elongation at break. Broad molecular weight distribution is advantageous only at the lower molecular weight range (650 and 1000), giving rise to improved resilience and low-temperature performance. Polyurethanes made from PTMEG of low molecular weight (Mn≤1000) have inherent drawbacks due to poor phase separation (high Tg) and limits in soft segment concentration (∼63% maximum for PTMEG 1000). The only advantage they offer is easier processability (lower viscosity and melting temperature). On the other hand, PTMEG above 2100 offers little property advantages and is more difficult to handle. Optimum overall polyurethane properties can be achieved with PTMEG in the molecular weight range of 1800 to 2100. It is conceivable that PTMEG-based polyurethanes made with different diisocyanates, curatives, curative/NCO ratios, or in the presence of triols or catalysts may show similar trends as the MDI/BDO formulations described in this study.
Fatigue Resistance of Natural Rubber in Compression
Authors: Lindley P. B. , Stevenson A.
Published: February 2011

Repeated deformation of natural rubber cylinders in compression causes cracks to initiate at points of maximum tensile stress concentration (e.g., at bond edges). These cracks grow until all the rubber which at the maximum deformation bulges outside the original profile of the cylinder is removed. Crack growth rates (da/dN) and strain energy release rates (G) have been determined. G is substantially independent of crack length. The relation between da/dN and G appears to be a fundamental material property for use in the determination of fatigue lives. Shaping the force free surface improves fatigue resistance.
Optimization of Rubber Mixing in Internal Mixers
Authors: Wiedmann W. M. , Schmid H. M.
Published: February 2011

Conventional rotor geometries of both the tangential and intermeshing systems can be improved in regard to working volume, feeding, mixing result, and milder temperature-rise. However it is necessary to consider both systems to supplement each other: (1) The tangential system is primarily for high machine efficiency, fast feeding, fast discharge and fast incorporation, i.e., for short mixing cycles and for multi-stage mixing. (2) The intermeshing system is for problems with distribution and temperature and for the increased theoretical output with longer mixing cycles by decreasing the number of mixing stages. Theoretical and experimental analysis of the influence of various operating parameters makes it possible to produce an optimum batch. The end result is process control which improves batch-to-batch uniformity.
The Application of Thermogravimetry (TG) to the Characterization and Quantitative Determination of Carbon Blacks
Authors: Charsley E. L. , Dunn J. G.
Published: February 2011

(1) The experimental variables which are found to affect significantly the measured T15 value for compounded carbon blacks are: (a) the maximum temperature achieved during the pyrolysis step and (b) the flow rate of air and the heating rate used during the oxidation step. (2) There is a definite correlation between the T15 value and the surface area of a carbon black, both in its free form and when compounded in a rubber. The T15 value is dependent on the cure method of the rubber and has also recently been reported to depend on the manufacturing source of the carbon black. This technique, therefore, cannot be recommended as suitable for the identification of a carbon black type in an unknown formulation. It can be used, however, as a routine quality control check on batch rubbers. (3) Thermogravimetry can be used as a rapid and accurate method for the determination of the carbon black content of rubbers, at levels as far apart as 0.1% and 30%.
Tackification Studies of Natural Rubber/Styrene-Butadiene Rubber Blends
Authors: Copley Bruce C.
Published: February 2011

A 50:50 blend of NR and SBR 1011 is heterogeneous. When tackified with a resin which is compatible with the NR phase, but not the SBR phase, the resin appears to partition unequally between the NR and the SBR. The resulting heterogeneous pressure-sensitive adhesives exhibit very broad storage modulus transition zones. The increased breadth occurs predominantly at the lower frequency portion of the transition. This is quite different from the NR/SBR blends tackified with a resin which is compatible with both NR and SBR. The NR/SBR blend with compatible resins exhibits a single sharp transition which is similar in character to either pure NR or pure SBR adhesives prepared with completely compatible resins. The differences due to heterogeneity are clearly manifested in the mechanical properties of the blend and are reflected by the rolling ball tack and shear strength to steel properties. Rolling ball tack data are consistent with the hypothesis that the NR phase is more highly tackified than is the SBR phase. Shear adhesion to steel data further support this conclusion.
Fundamental Flex Fatigue Studies of Tire Sidewall Materials
Authors: Young D. G. , Kresge E. N. , Wallace A. J.
Published: February 2011

1. Material, fabrication, and operating variables can be separately evaluated by the tearing-energy approach, and selection decisions are improved. 2. Results from a wide variety of laboratory and sevice conditions can be analyzed and compared by this general methodology. 3. Certain CIIR blend black sidewall compounds have inherent flex fatigue advantages over NR/BR compounds mainly due to their high levels of tearing energy sustainable before crack growth will begin. 4. The empirical approach used gives satisfactory cut-growth functions over a wide range of conditions with no need to assume the form of the function in advance. 5. Conventionally run fatigue-life experiments can be primarily influenced by maximum natural flaw sizes present and will not satisfactorily predict sidewall performance.
Analytical Characterization of Tackifying Resins
Authors: Lattimer R. P. , Hooser E. R. , Diem H. E. , Rhee C. K.
Published: February 2011

Phenolic resins are added to rubber compounds to improve the tack (or autohesion) characteristics. These resins are generally oligomers of alkylated phenols and formaldehyde. Analytical characterizations of these resins are very limited and incomplete in the open literature. We have examined several types of resins using mass spectroscopy (principally field desorption, FD-MS), liquid chromatography (LC), and infrared spectroscopy (ATR-IR). Several oligomeric series were identified by FD-MS in t-octylphenol and t-dodecylphenol resins. ATR-IR analysis showed that the t-octyl groups are essentially completely p-substituted on the phenolic ring. LC was only of limited utility in obtaining analytical separations of resin oligomers. Higher molecular weight oligomers (≿1500) showed little if any LC resolution. Resins prepared under different manufacturing conditions showed additional series of oligomers. These were either “cyclic ethers” and/or amine-containing compounds, depending on the synthetic procedures used.