bluuebunny/crossref_metadata_2025 huggingface dataset:
Tandem Mass Spectrometry (MS/MS) for Analysis of Organic Additives in an Uncured Rubber Compound
Authors: Lattimer R. P. , Muenster H. , Budzikiewicz H.
Published: February 2011

In this study, we examined the feasibility of obtaining MS/MS data for organic additives in an uncured rubber compound using several different ionization methods. EI-MS/MS worked well for those additives that gave intense molecular ions (M+·) via this mode of ionization. CI-MS/MS also worked quite well for most additives; the CI MH+ ion currents were generally quite intense and stable over a long period of time. Although fragmentation patterns for MH+ ions are different from those obtained from M+· ions, the fragments are still good diagnostic tools for identifying the original molecule. On the other hand, the FI- and FD-MS/MS analyses of these rubber samples were generally not very satisfactory. This was due to the fact that FI/FD ion currents were too weak and unstable to give daughter-ion spectra with good S/N. It may be concluded that the best way to detect and identify typical organic additives in a compounded rubber is to use a combination of EI- and CI-MS/MS. In this study, intact accelerators were successfully analyzed by MS/MS. The two accelerators in this particular rubber (OBTS and DPG) could be confirmed quite readily by daughter-ion analysis of their intense MH+ ions (CI-MS/MS). Daughter-ion analyses of M+· obtained by either EI, FI or FD modes were not very successful, however. In EI, the difficulty is that molecular ions are quite weak (or even absent) for typical rubber curatives. In FI and FD, on the other hand, a very large proportion of the ion current for accelerators resides in the molecular ion. The difficulty here is that the total ion current produced by FI or FD is rather low. The MS/MS approach has proven to be very useful for direct analysis of organic additives in rubber compounds. The principal advantage in using MS/MS is that more information is available from mixtures than can be obtained by direct analysis using conventional mass spectral methods. The MS/MS technique is also rapid experimentally compared to other techniques for mixture analysis such as GC/MS, LC/MS, or high resolution (AC-MS). Finally, since MS/MS involves two stages of mass analysis, it leads to a great reduction in the chemical noise associated with single-stage mass spectrometry. This leads to the facile confirmation of the presence (or absence) of specific components in a complex mixture.
Solid-State NMR of Elastomers
Authors: Kinsey Robert A.
Published: February 2011

The versatility of solid state NMR for the characterization of elastomers and elastomer composites has been demonstrated. NMR can be used as an analytical tool for identifying the elastomer(s) present (including the sequence distribution and tacticity), measuring crosslink levels, and monitoring chemical modifications. In addition, with relaxation measurements, NMR provides direct physical insight into the dynamics, and hence the spatial interactions of elastomeric systems. The interfacial regions of heterogeneous systems such as IPNs, filled elastomers, and block copolymers can be probed. A variety of NMR parameters can be correlated with physical properties. Future studies will extend the use of variable temperature and high magnetic field strength measurements, as well as utilize the growing number of two-dimensional experiments. The use of solid state H-l NMR should increase as instrumentation progresses, complementing the heteronuclear work. Solid H-l NMR offers significant sensitivity increases over C-13 NMR, but with decreased resolution. N-15 NMR studies have been recently performed at natural abundance with rigid polymers, and will likely be useful for characterizing elastomers.
A Novel Fluorocarbon Elastomer for High-Temperature Sealing Applications in Aggressive Motor-Oil Environments
Authors: Grootaert W. M. , Kolb R. E. , Worm A. T.
Published: February 2011

The tendency in the automotive industry to use smaller engines has resulted in a situation where lubricating oils are exposed to higher operating temperatures. This is especially the case in countries where there is no restriction on highway speed. Amine-based additives present in the oils (e.g., as dispersants and corrosion inhibitors) tend to slowly attack the conventional fluorocarbon elastomer seals under these conditions. As a result of that attack, the seal becomes brittle and eventually fails. A novel fluorocarbon elastomer of vinylidene fluoride, tetrafluoroethylene, and propylene has shown excellent aging behavior in the laboratory toward many aggressive engine oils at elevated temperature. Its improved resistance as compared to conventional fluorocarbon elastomers is attributed to the replacement of hexafluoropropylene with propylene.
Prediction of Bound-Rubber Modulus by Clausius—Mossotti Approximation
Authors: Scobbo J. J.
Published: February 2011

The Clausius—Mossotti approximation has been used to determine the modulus of bound rubber attached to carbon black in a gum-rubber/carbon-black compound. The effective hydrodynamic concentration of the carbon-black/bound-rubber structure was first determined based on the assumption of spherical filler particles with a uniform layer of bound rubber on the surface. The true carbon-black concentration was then subtracted from this concentration, and a three component modeling scheme was used. The three components were considered to be bound-rubber, carbon black, and gum-rubber matrix. The Clausius—Mossotti approximation was used to determine the bound-rubber modulus that would give the same compound modulus based on equivalent hydrodynamic volume. Results indicate that bound-rubber concentration decreases with increasing strain. At zero strain, the bound-rubber concentration is approximately equal to the carbon-black concentration. Modulus values of bound rubber were found to be 3 to 4 times greater than gum-modulus values at very low strains. The relatively greater magnitude of bound-rubber modulus decreased with increasing strain until the filler effect appears to be almost purely hydrodynamic. The electromagnetic theory-based Clausius—Mossotti model was found to predict bound-rubber moduli that were in agreement with a mechanical model, the Kerner model.
Reactively Curable Rubbers—I: Diene Elastomers with Pendant Isocyanate and/or Hydroxyl Functionality
Authors: Parker Dane K. , Colvin Howard A. , Weinstein Arthur H. , Chen Sun-Lin
Published: February 2011

In conclusion, we have demonstrated that modified diene elastomers containing active hydrogens and/or blocked-isocyanate derivatives can be crosslinked (cured) by three distinct methods. These methods include: 1. reaction of polymer-bound active hydrogens with monomeric polyisocyanates (Type I), 2. reaction of polymer-bound isocyanates with compounds containing two or more active hydrogens (Type II), and 3. reaction between polymer segments that contain both polymer-bound isocyanates and active hydrogens (Type III). Additionally, we have shown that the new polymerizable blocked-isocyanate derivatives (Type II and III systems) can be readily incorporated into SBR and NBR elastomers by standard emulsion-polymerization techniques. The degree and distribution of these monomers within the elastomer matrix were shown to be controlled by knowledge of their reactivity ratios. Furthermore, we have shown that the processing and properties of these systems can be readily controlled by the proper combination of isocyanate blocking group, active-hydrogen component, and catalyst. In many cases, these modified elastomers can be coagulated, dried, compounded, and cured using methods common to the rubber industry. Although not optimized, we have also shown that useful vulcanizates can be produced from extremely simple recipes. Conventional acceleration systems e.g., sulfur, accelerator, zinc oxide, are eliminated. The resulting urethane or urea crosslinks are remarkably durable under both thermal and hydrolytic conditions. Obviously, the possibilities for these uniquely reactive elastomers have not been exhausted. Many other intriguing applications of this technology are currently being explored. These applications will be the subject of future publications.
New Elastomers by Reactive Processing. Part I. Vulcanizable Precured Alloys from NBR and ACM
Authors: Coran A. Y.
Published: February 2011

The dynamic vulcanization of ACM (the dispersed phase) during its mixing with NBR (the continuous phase) can produce a new type of millable specialty elastomer alloy. The millable dynamic vulcanizate containing the crosslinked dispersed phase can be later mixed with curatives for the continuous phase, fillers, antidegradants, etc. The completed mixture of millable dynamic vulcanizate with the additional curatives (for the NBR), fillers, stabilizers, etc. can then be vulcanized e.g., in a heated mold. Thus, the dynamic vulcanization technique is a means of separately controlling the vulcanization of individual phases of a blend of elastomers. Since the ACM can be completely vulcanized during the dynamic vulcanization stage of the mixing process, the usual postcuring associated with ACM technology is not necessary. Also, since the continuous or external phase is NBR, the prevulcanized millable alloy exhibits processability more similar to that of NBR than to that of ACM. Sticking and splitting on the roll mill is less of a problem after dynamic vulcanization than before dynamic vulcanization. The dynamic vulcanization of the ACM can be achieved by using the soap-sulfur type or the diamine-generator type curatives during the mixing process at elevated temperatures. Compositions filled either with carbon black (N326) or silica (Hisil 233) give compositions of excellent hot-oil resistance and room-temperature set. (Compression-set testing has not yet been done at this early stage of our research.) As in the case of conventional NBR stocks, the silica-filled compositions give excellent hot-air resistance whereas, carbon-black-filled compositions give fair hot-air resistance. In either the black-filled or the silica-filled compositions, provided that at least half of the rubber polymer is ACM, essentially complete resistance to ozone attack is obtained.
Effect of Contact Time on Tack
Authors: Gent A. N. , Kim H. J.
Published: February 2011

The following conclusions are obtained: 1. The autohesion strength of elastomers increases linearly with the rate of detachment over the range 200 to 1000 mm/s. 2. The autohesion strength increases by a factor of only 2× to 3× when the contact pressure is increased by 3 orders of magnitude, from 2 kPa to 2 MPa. 3. Autohesion strength develops rapidly in the early stages of contact for SBR, BR, and EPR, increasing from about 20 J/m2 to about 500–1000 J/m2 as the contact time increased from 1 to 100 ms. It increased more slowly thereafter, to about 10 kJ/m2 after a contact time of 1000 s. 4. The development of autohesion was exactly the same at 3°C as at 25°C. This feature is attributed to simultaneous changes in developing true contact, and in resisting separation after contact, that exactly cancel. 5. Adhesion between SBR and EPR is lower than the autohesion strength of the individual polymers over the whole range of contact time. On the other hand, the three strengths for SBR and BR are almost the same. 6. The overall similarity between the rates of development of autohesion and adhesion suggest that autohesion is governed mainly by the strength and extent of intimate molecular contact that is developed at the interface. Contributions from interdiffusion, if any, appear to be significant only in the later stages of contact.
Grafting of Waste Rubber
Authors: Adam G. , Šebenik A. , Osredkar U. , Veksli Z. , Ranogajec F.
Published: February 2011

By the redox method and by gamma irradiation, it was possible to graft ethyl acrylate on to granulate of waste rubber. The quantity of grafted monomer was larger when gamma irradiation was used. When combining ethyl acrylate with 5-methylene-2-norbornene in the redox system with the intention to introduce more double bonds in the grafted granulate, it was found that norbornene does not participate in the reaction and that it even prevents the grafting of ethyl acrylate. This is just a part of extensive experimental work which was done with the intention to chemically modify the rubber granulate for the purpose of enlarging the quantity of waste rubber to be possibly reused in the rubber industry.
Surface Treatments to Reduce Friction: Rubber Glove Applications
Authors: Roberts A. D. , Brackley C. A.
Published: February 2011

The frictional properties of rubber surfaces modified by various treatments have been investigated in order to understand the factors which reduce the friction and give the surface appropriate qualities for practical use. The study was in two stages. Initial measurements were made on thin sheets of hot-vulcanized natural rubber; then followed tests on latex glove material to see how the initial results and understanding related to the application. Measurements of friction coefficient were made against a wavy glass plate, giving reproducible results, and against finger skin. Supplementary measurements were made of surface roughness and hardness, liquid contact angle, and water absorption. Factors of importance in the reduction of dry friction were found to be an increased surface roughness and hardness. In practice, difficulties may be experienced under slightly wet or damp conditions, which can increase the friction above the dry value. Here it was found to help if the surface treatment could absorb water. For surgeons' gloves in contact with moist skin, one particular treatment, a hydrogel polymer coating, gave the necessary surface roughness, hardness, and water absorptivity, making the gloves easy to don and pleasant to wear.
Characteristic Ratio and Plateau Modulus of 1,2-Polybutadiene. A Comparison with Other Rubbers
Authors: Roovers Jacques , Toporowski Paul M.
Published: February 2011

In the course of work on linear and ring polybutadienes with 62% 1,2 units, a number of discrepancies were noted with data on polybutadienes of various microstructure available in the literature. For example, GNο=870 kPa for our 62% 1,2-polybutadiene. This is larger than GNο=730 kPa for a 56% 1,2-polybutadiene and GNο=550 kPa for a 78% 1,2-polybutadiene sample. The cis : trans ratio of our 62% 1,2-polybutadiene, prepared with potassium counterion, is 1 : 4, On the other hand, the cis : trans ratio of 62% 1,2-polybutadiene prepared with a modified Li catalyst is estimated to be 1 : 2. It is conceivable that the different cis : trans ratio leads to different properties at constant 1,2 content. Nevertheless, the low levels of both the cis and the trans units are not expected to cause more than minor differences in the properties of the polybutadienes. Correct values for GNο of model polymers are important for the study of the influence of the chemical structure on the melt characteristics of a polymer. For this reason, it was thought useful to reinvestigate 1,2-polybutadiene itself in some detail. The synthesis of narrow molecular-weight distribution 1,2-polybutadiene by anionic polymerization techniques has been described recently. The dilute-solution properties of 1,2-polybutadiene has been investigated. The melt rheology of two 1,2-polybutadiene samples have been studied, but no systematic study of the molecular-weight dependence of the melt properties was made. 1,2-Polybutadiene has been used as a component in block copolymers with 1,4-polybutadiene. These studies have permitted an investigation of the phase behavior of two rubbery blocks at room temperature. Poly(l,4-butadiene-graft-l,2-butadiene)s with well-defined composition and architecture have also been prepared. Hydrosilylated 1,2-polybutadiene has found use as the coupling agent for multiarm star polymer, and this method can easily be extended to the preparation of poly( l,2-butadiene-graft-l,4-butadiene). Hydrogenated 1,2-polybutadienes are prepared as model polymers for poly(l-butene). The synthesis and characterization of a series of 1,2-polybutadienes are described here. Special attention is given to low-molecular-weight polymers. The linear viscoelastic properties of the melts are also described. In the discussion, the relation between the characteristic ratio, C∞, and the plateau modulus, GNο, of a number of model polymer systems is explored.
The Resolution of Elastomer Blend Properties by Stress-Strain Modelling. An Extension of the Model to Carbon-Black-Loaded Elastomers
Authors: Bauer R. F. , Crossland A. H.
Published: February 2011

The unique stress-strain behavior of a carbon-black-loaded elastomer is due to the presence of a rigid, particulate phase, but also to the interaction of the elastomer chains with the filler. It is postulated that this interaction takes the form of adsorption on the filler-particle surface, which results in trapped entanglements. Upon deformation, the trapped chains are aligned parallel to the axis of stress. Thus, a practical stress-strain relationship could be developed which is capable to model the stress-strain behavior of compounds over the full range of extensions up to break. The analysis of a highly prestrained carbon-black-loaded NR compound in which the entanglement effect had been mechanically destroyed, demonstrated that the “sea-island” (SIP) coupling arrangement is most suitable for accounting for the interaction effect of the elastomer and carbon black. For moderately prestrained carbon-black-loaded NR and BR compounds a good fit of theory to experiment is obtained for a combination of the SIP coupling arrangement and the specially derived stress-strain relationship. Thus, a practical method is available for describing the deformation of carbon-black-loaded elastomers and for the modelling of carbon-black-loaded elastomer blends.
Mechanical Properties of Vulcanizates Containing Covalent, Ionic, and Mixed Crosslinks
Authors: Hamed Gary R. , Han K. T.
Published: February 2011

Vulcanization by peroxide and sulfur are the two common methods to crosslink diene elastomers. Crosslinks using peroxide are simple carbon-carbon covalent bonds, whereas, with sulfur, a distribution of sulfur linkages, Sx, of various rank, x, may be present. Networks in which x=1 exclusively are said to be monosulfidic; these, as well as peroxide-cured vulcanizates, possess low-set characteristics, low stress relaxation, and good resistance to aging—all evidence of the permanence of C-S-C and C-C linkages. On the other hand, when x is large, the networks are termed polysulfidic; stress relaxation and set are higher, while resistance to aging (network stability) is poorer compared to rubbers with monosulfidic or carbon covalent linkages. It has been proposed that these properties result from the relative weakness of polysulfide bonds, which can break and reform under load. In applications such as tires, where resistance to fracture under severe loads is required, accelerated-sulfur vulcanization with sulfur is the preferred method of crosslinking. These networks are neither completely monosulfidic nor fully polysulfidic, but rather contain a mixture of weak and strong crosslinks. The distribution depends on the type and level of accelerator, the sulfur concentration, and the curing conditions. It is quite difficult to characterize this distribution, or even approximately to infer it from the complex chemistry of sulfur vulcanization. Trial and error methods, over the years, have led to optimized compositions. Vulcanizates with the appropriate mix of crosslink types have superior strength and fatigue resistance compared to networks containing only permanent links, i.e., carbon-carbon covalent or monosulfidic. Perhaps the important feature which has allowed sulfur vulcanization to remain the dominant crosslinking method for over 100 years is the presence of crosslinks with varying strength.
Multifunctional Activities of Benzazole Derivatives in Rubber Vulcanization
Authors: Khanra Tapan Kumar , Adhikari Basudam , Maiti Sukumar
Published: February 2011

Benzazole thiol (e.g. 2-Mercaptobenzothiazole and 2-Mercaptobenzimidazole) and sulfenamide (e.g. 2-Morpholino thiobenzothiazole) are used as rubber chemicals. The nature and the extent of their performances in rubber depend on the nature of the key heteroatom present in the azole ring. It has been found that the presence of X (S or N) as the key heteroatom in the grouping —X—‖—SH of the azole ring is responsible for either accelerator or antioxidant action. Although some scattered informations on accelerator and antioxidant functions are available for some of the benzazole derivatives, their comparative ratings in these functions are not found in the literature. In the present communication, synthesis and characterization of some benzazole sulfenamides are reported. Together with this, a comparative evaluation of accelerator-cum-anti-oxidant properties of both the benzazole thiols and sulfenamides is described. Such dual function rubber chemicals are unusual and novel and should fetch a premium price as rubber additives.
The Influence of Fumed Silica Properties on the Processing, Curing, and Reinforcement Properties of Silicone Rubber
Authors: Cochrane H. , Lin C. S.
Published: February 2011

The present study uses a commercial heat cured silicone rubber formula (including a process aid) and mixing techniques to investigate the effect of varying fumed silica properties—including load, surface area, silica structure level, and surface pretreatment levels—on the rubber processing, curing, and cured physical properties. Based on the results, a simple silica network reinforcement model was developed to explain the changes in processing, curing, and vulcanizate properties of the silicone elastomers. The network is held together by silica-silica interactions and silica-polymer-silica bridge bonds between the silica aggregates. Increasing the silica loading, surface area, and structure level increases the number of interactions and hence the network strength. The pretreatment of the silica surface with organosilane molecules reduces the strength of silica-silica and silica-polymer interactions, therefore, weakening the silica network. Furthermore, the good interrelations between the initial plasticity, crepe hardening, curing, modulus yield, and durometer values strongly supports the concept of the presence of a silica network within the compounds under the low strain conditions of the tests.
Solid State C-13 NMR Studies of Vulcanized Elastomers. XII. Accelerated Sulfur-Vulcanized High-Vinyl Polybutadiene
Authors: Rana M. A. , Koenig J. L.
Published: February 2011

Solid state 13C NMR measurements were made on accelerated sulfur-vulcanized polybutadiene with a high vinyl content (70%). The systems studied included conventional, semi-efficient and efficient formulated with N-t-butyl benzothiazole sulfenamide (TBHS) as the accelerator. The kinetics of the three vulcanization systems were different, but the final levels of cure were similar. The resonances due to TBBS disappear as the vulcanization proceeds. The ratio of monosulfidic to polysulfidic crosslinks as a function of accelerator to sulfur ratio initially decreases rapidly and then increases in favor of the monosulfidic component. A variety of sulfur-bonded accelerator fragments was found in the system. This reinforces the polar-radical mechanism.
The Development of Elastomer Rheological Processability Quality Control Instruments
Authors: White James L. , Soos Istvan
Published: February 2011

We have surveyed the development of processability measurements from its origins, about 1920, to the present. We have followed the factors—technology, scientific, and political—which have caused its evolutions. The earliest instruments the capillary and compression rheometer, are still with us. As early as the mid 1930s, different traditions developed in the United States and Germany, differences which continue to the present day. These were accentuated by the development of synthetic rubber and World War II. The Germany industry used the Defo compression instrument and the Americans decided on the Mooney shearing disc viscometer. The early postwar period saw a temporary withdrawal of German activity and an American interest in stress relaxation measurements with a biconical stress relaxation instrument being made semi-commercial by B. F. Goodrich in the 1970s. B. F. Goodrich has continued to improve this instrument over the past generation. The post-1975 period has also seen increased activity in Germany; Bayer AG(i) redesigned the Defo instrument and had it commercialized by Haake and (ii) devised a Mooney post-shearing stress relaxation measurement which has been commercially developed by Monsanto. A pressure-controlled rotational rheometer has been developed by Avon Rubber which allows for better study and characterization of slip. The development of instruments has been coupled with growing knowledge of the rheological properties of gum elastomers and carbon black compounds.
Practical Chemical Blowing Agents for Expanding Rubber
Authors: Rowland Donald G.
Published: February 2011

The most effective chemical blowing agents for producing cellular rubber products are ADCA, activated forms of ADCA, OBSH and DNPT. Blends of ADCA types and OBSH are also used quite extensively. These blowing agents may be used to make automotive weatherstripping, various types of athletic padding, insulation and flotation materials as well as numerous other expanded products.
The Effect of Zinc Distribution on the Mechanical Stability of NR Latex Concentrates
Authors: Davies R. T. , Pendle T. D.
Published: February 2011

Dithiothreitol (DTT) has been found to increase the mechanical stability of natural rubber (NR) latex concentrates, particularly in the case of low ammonia TZ (LATZ) latices. The DTT interacts with the zinc on the rubber particle surface to form an insoluble phase which then precipitates in the sediment phase of the latex. Zinc ions tend to destabilize latex by neutralizing some of the fatty acid anions and proteinate anions on the rubber particle surface and DTT increases the stability of latex by removing a large proportion of these zinc ions. The metal complexing agent EDTA is even more effective than DTT at increasing the mechanical stability of LATZ latex. EDTA removes all the zinc from the particle surface and also solubilizes zinc in the sediment, possibly liberating fatty acid anions from the sediment which could then stabilize the latex further. This effect may be useful because it provides a means of increasing or maintaining the stability of LATZ latex when addition of a surfactant is undesirable EDTA also improves the storage stability of a typical post-vulcanizable latex mix which contains zinc—added in the form of zinc oxide—and an accelerator.
The Efficiency of Peroxides for Curing Silicone Elastomers
Authors: Class J. B. , Grasso R. P.
Published: February 2011

Peroxides are preferred for heat curing vinylmethylsilicone (VMQ) elastomers because the free-radical-initiated crosslink does not reduce the inherent stability of the polymer. The objectives of this work were (1) to obtain information on the relationship between peroxide concentration and the physical properties of heat-cured silicone elastomers, and (2) to explain the suspected difference in efficiency of two peroxides, α,α′-di(tert-butylperoxy)-m/p-diisopropylbenzene (DBPIB) and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DBPH). VMQ bases and gums were cured with DBPIB and DBPH over a range of peroxide concentrations. Higher tensile modulus and higher delta torque (oscillating disk rheometer data) were observed when curing with DBPIB over the entire concentration range. This indicates that DBPIB produces a higher crosslink density than DBPH at equivalent molar concentrations. A series of calculations were performed, using computational chemistry techniques, to gain insight into the reason for the observed difference in crosslinking efficiency between DBPIB and DBPH. These calculations show that DBPIB is not more efficient than DBPH in abstracting hydrogen from the methyl groups of sihcone elastomers. The predominant cause for the difference in efficiency is related to the stability of the DBPH free radical. This radical is formed from hydrogen abstraction at the central ethylene moiety of DBPH by neighboring peroxy fragments. Therefore, DBPH is more susceptible to hydrogen abstraction, which consumes radicals in nonproductive (noncrosslinking) pathways This difference in peroxide efficiency may apply to other polymers.
2-(Isopropylsulfinyl)-Benzothiazole as a Delayed Action Thiazole Accelerator
Authors: Hopper Roger J.
Published: February 2011

At vulcanization temperatures, 2-(isopropylsulfinyl)-benzothiazole(ISB) generates 2-benzothiazole sulfenic acid as a reactive intermediate. In this respect (i.e., formation of a sulfenyl species), ISB is analogous to a benzothiazole sulfenamide, but without the built-in amine activation. Thus, ISB alone is slow, but responds to a variety of activators. The potential to independently select the activator can offer a wider latitude in meeting today's compounding challenges. For example, ISB activated by tetrabenzylthiuram disulfide represents a system devoid of precursors of volatile introsamines ISB with thiophosphoryl sulfides can provide effective, amine-free cure packages. Where nitrosamines are not a factor, tetramethylthiuram monosulfide (TMTM) remains the best general purpose activator. Examples of the effects of ISB/activator systems on cure characteristics and physical properties in a variety of recipes are presented. A unique, practical synthesis of ISB in two steps from MBT, propylene and bleach is outlined, and a more generally adaptable laboratory procedure is described in detail. Diagnostic reactions of ISB and substituent effects of related derivatives, designed to support the postulated acceleration mechanism, are described.
GPC Calibration for the Molecular Weight Measurement of Butyl Rubbers
Authors: Puskas Judit E. , Hutchinson Rob
Published: February 2011

Size Exclusion Chromatography (SEC) or Gel Permeation Chromatography [GPC] was used to determine the molecular weight and molecular weight distribution of butyl rubbers. Quantitative data were obtained by viscometry, and by the use of narrow distribution polyisobutylene (PIB) standards for calibration. The application of the Universal Calibration Principle, which uses readily available narrow distribution polystyrene (PS) standards, relies on the knowledge of the Mark-Houwink-Sakurada constants, K and α, for PIB or butyl rubber (the copolymer of isobutylene and isoprene containing 1–3 mol% of the latter). Comparison of narrow PIB and narrow PS calibrations led us to the selection of KPIB=2×10−4 dl/g and α=0.67, the constants published by the American Standards Corporation for PIB in tetrahydrofuran (THF) at 30°C, as best fit values. The weight average molecular weight [Mw] of various samples of commercially produced butyl rubber determined by using the Universal Calibration Principle with the selected constants, agreed well with those measured by viscometry. Other published K and α values yielded a poorer agreement.
A Constraint Dynamics Approach to Rubber Elasticity
Authors: Ngai K. L. , Roland C. M. , Yee A. F.
Published: February 2011

The coupling model of relaxation is applied to crosslinked rubber, with a connection drawn between the dynamics of network junctions and statistical mechanics derived rubber elasticity theory. The suggestion that unifying concepts must underlie dynamical models and thermodynamic theories is shown to be supported by analyses of recent 31P NMR spectroscopy measurements by Shi, Dickinson, MacKnight and Chien on polytetrahydrofuran networks and of our mechanical relaxation data on stretched and unstretched polycarbonate.
An Analysis of the “Durometer” Indentation
Authors: Briscoe Brian J. , Sebastian K. Savio
Published: February 2011

The mechanics of the indentation of elastomers by the “Durometer” (Shore A) hardness tester is analysed using the theory of elasticity to derive an interrelation between the Shore hardness number and the Young's modulus. Experimental compliance curves, for different elastomers, are provided to support the theory. The theoretical interrelationships between the International Rubber Hardness and the Shore A Hardness and the corresponding elastic modulus are also compared. The effects of the time dependent deformations are examined. Finally, the error introduced by computing the Young's modulus using an equivalent punch solution is examined and a means of improving the predictions is provided.
Ultrasound Devulcanization of Sulfur Vulcanized SBR: Crosslink Density and Molecular Mobility
Authors: Levin V. Yu , Kim S. H. , Isayev A. I. , Massey J. , von Meerwall E.
Published: February 2011

Sulfur-cured SBR vulcanizates are devulcanized by high power ultrasonic irradiation in a continuous process under various processing conditions. Crosslink density and gel fraction of devulcanized rubber are measured. The unique dependence of crosslink density on gel fraction of devulcanized samples obtained at various processing conditions is established. DSC studies indicate a significant increase in the glass transition temperature of the devulcanized rubber having crosslink density lower than that of the original vulcanizates. Solid state NMR studies confirm that these changes in Tg are due to a decrease of molecular mobility as measured by a decrease in spin-spin relaxation time. Ultrasonic devulcanization is accompanied by a significant increase in xcis-trans isomerization. Chemical changes explaining the observed phenomena are discussed.
Mechanism by Which Precipitated Silica Improves Brass-Coated Wire-To-Natural Rubber Adhesion
Authors: Waddell Walter H. , Evans Larry R. , Goralski Edward G. , Snodgrass Linda J.
Published: February 2011

Quantitative determination of elements in the interfacial growth layer formed on brass-coated wire when reacted in squalene suspensions containing carbon black and curatives, with and without precipitated silica and an organocobalt adhesive, was accomplished by using direct surface characterization techniques: Scanning Electron Microscopy with Energy Dispersive Analysis of X-rays (SEM-EDX), Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS) and Proton Induced X-ray Emission (PIXE) Spectroscopy. The effects on elemental changes in the interfacial growth layer upon addition of silica and/or cobalt neodecanoate to the squalene suspensions were statistically analyzed. Since the mechanism for silica improvement of brass-coated wire-to-rubber adhesion was previously shown not to be a simple effect of improving rubber physical properties, a chemical mechanism is proposed involving silica to reduce the thickness of the interfacial growth layer and to change the relative concentration of compounds formed in the interfacial growth layer.
A Study of the Vulcanization Kinetics of an Accelerated-Sulfur SBR Compound
Authors: Ding R. , Leonov A. I. , Coran A. Y.
Published: February 2011

Vulcanization kinetics for a SBR compound was studied by using both curemeter and DSC methods by a kinetic approach. A simplified but realistic model reaction scheme was used to simulate both induction and curing periods simultaneously. Model parameters were extracted from isothermal curemeter experiments. The model prediction demonstrated a good agreement with isothermal curemeter data over a temperature range of 120°C to 180°C. The variation of equilibrium modulus with temperature, observed from cure curves, can also be predicted. However, DSC experiments showed a different reaction behavior in the curing period as compared to model calculations. This was explained by the assumption that the reaction heat observed in DSC is due to all possible exothermal reactions, and the formation of crosslinks is only a part of these reactions. Hence, the curemeter can provide a good indication of crosslink formation, while DSC displays the entire reaction heat released during the vulcanization process. The kinetic approach allows one to incorporate vulcanization kinetics into the practical simulation of reactive processing operations.
A Simple Methodology for the Modeling of Carbon Black Aggregate Structure
Authors: Li Qi , Manas-Zloczower Ica , Feke Donald L.
Published: February 2011

A procedure for modeling some morphological characteristics of carbon black aggregates is presented. The method uses a standard reaction limited aggregation algorithm to predict the location of the centers of primary particles within an aggregate. The shape of the aggregate is determined by drawing simple linear links between extreme points of primary particles centered on these loci. Analysis of the particle distribution function computed from the simulated structure leads to definitions of the interior and periphery of the aggregate structure. Direct comparisons between simulated aggregates and two commercial carbon blacks are presented to illustrate the usefulness of the approach. The perimeter fractal dimension of simulated aggregates can be made to match the perimeter fractal dimension of the commercial carbon black aggregates through proper choice of the sticking probability in the simulation algorithm. With this proper choice of sticking probability, the relative amounts of voids in the periphery and interior of the simulated aggregate correspond to relative amounts of filled and unfilled voids in actual aggregates that have been soaked for extended periods of time with processing fluids.
Devulcanization of Waste Tire Rubber by Powerful Ultrasound
Authors: Tukachinsky A. , Schworm D. , Isayev A. I.
Published: February 2011

Ground rubber tire (GRT) is devulcanized in a continuous process where the rubber crumb is conveyed by a screw extruder to a thin gap between a stationary die and a vibrating horn. Ultrasound amplitude, gap thickness and the duration of the treatment are varied, and their effect on the rubber properties is studied. The degree of devulcanization is characterized by the crosslink density and gel fraction of the devulcanized rubber. These characteristics are found to correlate uniquely with each other over a wide range of the treatment conditions. The specific energy of ultrasound consumed per unit mass of the rubber is found to be the operating parameter correlating with the properties of the devulcanized rubber. The mechanical properties of the re-vulcanized samples reach a maximum with an increasing degree of devulcanization, and then drop as a result of excessive degradation. Even without optimization of cure recipes, tensile strength and ultimate elongation of re-vulcanized tire rubber as high as 10.5 MPa and 250%, respectively, are achieved.
Novel Sulfur Vulcanization Accelerators Based on Mercapto-Pyridine, -Pyrazine, and -Pyrimidine
Authors: Rostek Charles J. , Lin Horng-Jau , Sikora David J. , Katritzky Alan R. , Kuzmierkiewicz Wojciech , Shobana Navayath
Published: February 2011

Sulfur vulcanization accelerators derived from 2-mercaptobenzothiazole (MBT) have been a staple for the rubber processing industry for over 65 years. Most noteworthy are the sulfenamide derivatives, which provide various combinations of scorch delay and cure rate, depending upon the basicity and steric nature of the sulfenamide N-substituent(s). While the effect of the amine moiety on benzothiazole sulfenamide accelerator performance has been well documented, the effect of the S-linked heterocyclic moiety of the sulfenamide has been investigated to a much lesser extent. Thus, to gain a better understanding of the role of the heterocycle, a variety of novel disulfides and sulfenamides based on pyridine have been synthesized and tested. The performance of the pyridine based accelerators have been compared to each other and to the various benzothiazole analogues. Until recently, the corresponding sulfenimides (compounds containing two divalent thiol moieties attached to an amine nitrogen ) seem to have received little attention in the rubber industry. Sulfenimides based on pyridine, pyrazine and pyrimidine have therefore also been synthesized and tested. The differences in preparation and vulcanization activity for the benzothiazole sulfenimides and sulfenamides are described, as well as some rudimentary differences which have appeared in the early stages of mechanistic work. It has been discovered in the course of this work that other heterocyclic thiols may be substituted for 2-mercaptobenzothiazole in the basic sulfenimide structure to gain advantages both in faster cure rate and extended scorch delay. The behavior of these novel sulfenimides in common rubber cure systems is presented together with representative physical properties of the rubber vulcanizates.
Effect of Porosity on Dynamic Mechanical Properties of Rubber in Compression
Authors: Kasner Alan I. , Meinecke Eberhard A.
Published: February 2011

Cylindrical samples of different levels of porosity were prepared from a model carbon black filled rubber and tested in compression. Dynamic properties were determined with dynamic loads and dynamic displacements superimposed on static loads. Nonlinear stress-strain curves of porous rubber blocks produced a dependence of dynamic properties on the mode of testing. Both storage and loss moduli as well as tan γ were found to depend on the levels of porosity. The loss modulus was found to increase with higher strain levels in porous samples, while the storage modulus changed because of reduced sample stiffness. The dynamic data was in agreement with the results of Goodrich flexometer tests on porous and solid samples. The results suggest that the introduction of porosity reduces service life of rubber parts by providing stress raisers for crack initiation, rather than through changing the dynamic properties.
Reinforcement Mechanisms in Carbon Black and Silica Loaded Rubber Melts at Low Stresses
Authors: Eggers H. , Schummer P.
Published: February 2011

For a range of different fillers, silicas and carbon blacks, added to a rubber melt at various concentrations, dynamic moduli in the linear viscoelastic limit have been determined. It is shown that reinforcement is due to hydrodynamic effects and the formation of a secondary particulate structure within the rubber matrix. Both mechanisms can be distinguished experimentally by a frequency sweep. Hydrodynamic reinforcement depends on the filler volume to which immobilized polymer must be added. Its concentration dependence is well described by the semiempirical exponential Thomas Equation. Nominal and effective filler loadings are related by concentration-independent effectiveness factors which can be modelled for all types of fillers considering an immobilized layer of constant height around an agglomerated cluster of filler particles. This provides an explanation for the well-known dependence of reinforcement ability on surface area at small stresses. The chemical and microscopic structure of the filler surface appears to be less important with respect to immobilization ability in the linear viscoelasic regime. The secondary structure formed by the particles is found to be tied together by the elastomer. Its modulus correlates with the filler's immobilization ability and shows little dependence on the filler nature. Due to formation of a filler-polymer structure with individual relaxation times, a strict separability of hydrodynamic and interparticular-reinforcement mechanisms at very high loadings no longer applies.
The Rolling Resistance, Wear and Traction Properties of Tread Compounds
Authors: Grosch K. A.
Published: February 2011

The paper gives a brief survey of the state of friction and abrasion research with a view of the possibility to use laboratory methods for the development of new compounds with optimal traction and abrasion properties. It shows that viscoelasticity plays a decisive role in friction and in this way measurements of the dynamic properties give a good indication of the possibilities for good traction properties. However, friction is still a good deal more complex than the modulus or loss factor curves. It takes in different frequency ranges and temperatures in the contact area so that a direct laboratory measurement of these properties is still very desirable. If the speed and temperature correspond to the log aTv values experienced in practice and the laboratory track structure and texture is not too far removed from that of road surfaces, the correlation with road tests is high. To simulate the structure and texture of road surfaces with durable laboratory surfaces, a combination of two surfaces may be necessary. Abrasion is not only influenced by the strength properties of the rubber but also by oxidation and thermal degradation. To give these processes the correct weight in the laboratory, the testing conditions have to be mild and a combination of several conditions is necessary in order to demonstrate the complexity of interactions, which can lead to ranking reversals. Energy dissipation, speed, and abrasive surface structure and texture are identified as prime variables to achieve a high correlation with road wear. Since viscoelasticity, encompassing not only polymer but also filler, oil-extension, curing and other compound additives, plays a major role in both friction and wear, the rolling resistance of the compound is always effected and has to be taken into account. Modern polymerization methods and new filler concepts make it possible to change the viscoelastic properties in such detail that high friction and—to the degree to which strength contributes to wear—high wear resistance can be combined with low rolling resistance. This development has certainly not reached its climax yet. Exciting times lie ahead for tire compounders, polymer- and filler chemists alike.
Intrinsic Defects and the Failure Properties of cis-1,4-Polyisoprenes
Authors: Choi I. S. , Roland C. M.
Published: February 2011

Inherent flaw sizes were determined from fatigue lifetimes, and from the crack length dependence of the strain energy to break, for four cis-1,4-polyisoprenes compounded to have the same crosslink density and low strain hysteresis. Both techniques indicated that the flaws intrinsic to guayule rubber (GR), and to a lesser extent conventional natural rubber, are larger than those found in deproteinized NR. This result may not be surprising; however, the failure properties of the elastomers, expected to depend on flaw size, were surprising. The guayule rubber and a natural rubber of relatively low purity (SMR-10) had the highest tensile strengths, tear strengths, breaking energies, and fatigue lifetimes, while DPNR exhibited the worst failure properties. Such an inverse correlation between flaw size and failure performance is due to the dominant effect of strain-induced crystallization. GR and SMR-10 have the highest propensity for strain-induced crystallization, while DPNR is the least strain-crystallizable. Interestingly, all rubbers exhibited the same isotropic crystallization behavior.
Origin of Characteristic Properties of Natural Rubber—Synergistic Effect of Fatty Acids on Crystallization of cis-1,4-Polyisoprene: II, Mixed and Esterified Fatty Acids in Natural Rubber
Authors: Nishiyama Naoyuki , Kawahara Seiichi , Kakubo Takashi , Hwee Eng Aik , Tanaka Yasuyuki
Published: February 2011

Crystallization behavior of deproteinized natural rubber at −25°C was investigated by dilatometry in connection with the effect of long-chain fatty acid groups, esterified to the rubber chain, as well as free fatty acids and their esters. The overall crystallization rate decreased after removal of the acetone-extractable free fatty acids and their esters, while it increased significantly when the fatty acid groups esterified to natural rubber molecule were removed by transesterification with sodium methoxide. Both the acetone-extracted and transesterified rubbers showed a significant increase in the overall crystallization rate after the addition of 1 wt % stearic acid. The crystallization of acetone-extracted rubber was accelerated by the addition of 1 wt % methyl linoleate, a plasticizer of natural rubber, whereas it was suppressed in the case of transesterified rubber in which the esterified fatty acid groups were removed completely. The fatty acid groups esterified to natural rubber molecule gave rise to the accelerated crystallization of the rubber in conjunction with free fatty acids and their esters.