bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Modulus, High Damping, High Fatigue Life Elastomer Compounds for Vibration Isolation
Authors: Lemieux Marvin A. , Killgoar Paul C.
Published: February 2011

NR/BR/NIR copolymer blends were found to be too stiff at low temperatures for many potential isolation applications. Soft compounds have been developed which exhibit high damping, long fatigue life, and good heat resistant properties. These compounds are based on NR/BIIR blends with IM as a diluent. The new compounds are cured with a semi-EV cure system. The morphology appears to be an important factor controlling the fatigue properties of the blends. Fatigue life can be affected by the cure temperature, molecular weight of the IM used, and by the use of amine anti-oxidants. For improved processing and shelf-life stability, the use of amine anti-oxidants is not recommended.
The Chemistry of the Zinc Oxide Cure of Halobutyl
Authors: Kuntz I. , Zapp R. L. , Pancirov R. J.
Published: February 2011

The studies described in this papier lead to certain conclusions. The crosslinking reaction of halobutyl with zinc oxide does not give rise to ether crosslinks. All the evidence indicates that the chemistry involves the formation of carbon-carbon bonds by an alkylation type chemistry. The dehydrohalogenation of the halobutyl to form a zinc chloride catalyst is a key feature of the crosslinking chemistry. But conjugated diene butyl and Diels-Alder reactions are not the major reaction pathway for the zinc oxide crosslinking reaction. These conclusions have significance for the zinc oxide cure of CR which has an active allylic halide structure formed by 1,2-monomer enchainment.
Trowelable Rubber Rocket Insulation for Use at 2800°C
Authors: Sommer J. G.
Published: February 2011

Ablative, trowelable rocket insulation was prepared; it crosslinks at room temperature and self-bonds to prevulcanized NBR insulation. The material loss rate (MLR) of this insulation is low when it is tested by an oxyacetylene torch at temperatures of about 2800°C. Boric acid in the insulation causes an effective char to form at service temperature. This char slows the loss rate of nondegraded insulation beneath it. Density of this nondegraded insulation is 1.3 g/cm3. Density is reduced sharply to 0.8 g/cm3 by incorporating glass microballoons. They cause only a slight increase in MLR of the insulation at service temperatures. MLR can be significantly reduced by incorporating a blowing agent which decomposes only after the insulation is exposed to service temperature. Hence, an unusual combination of requirements is met by several novel approaches. This insulation has protected rockets as large as 6.6 meters in diameter from the intense heat of burning propellant in service.
Identification of Rubber Additives by Field Desorption and Fast Atom Bombardment Mass Spectroscopy
Authors: Lattimer Robert P. , Harris Robert E. , Ross Doyle B. , Diem Hugh E.
Published: February 2011

From the results presented here, it is clear that FD-MS and FAB-MS are very effective analytical methods for the identification of organic additives in extracts from rubber compounds. In the examples above, the molecular weight information provided by FD and FAB provided a nice complement to the IR data. In cases where IR could give only a general answer (i.e., a compound class), the mass spectral data provided a very specific compound identification. It is encouraging that all the samples examined gave useful spectra by both FD and FAB analysis. In most cases, the same information was obtained by both techniques. Certain compounds, however, were observed by FD but not by FAB (wax, oil, isocyanurate antioxidant). While FD provided only molecular weight information, FAB also provided fragmentation to aid in the confirmation of component assignments. Both the FD and FAB mass spectra were fairly complex for most of the extracts, but for different reasons. In FD, oil and wax oligomers gave many molecular ions over a wide mass range. FAB spectra, on the other hand, were somewhat cluttered due to the normal background ions produced by the sputtering process. With both techniques, however, the various components in some fairly complex mixtures were readily identified.
The Bonding of Polychloroprene to Brass: Rate and Temperature Effects
Authors: Hamed G. R. , Liu F-C.
Published: February 2011

The bonding of CR to brass shim has been studied at various test temperatures and rates using a T-peel geometry. Compounds without sulfur adhere relatively weakly to brass, and the bond strength is highly temperature dependent. The bonding strength is greatly enhanced, and its temperature dependence decreased, if the CR contains only a minute amount of sulfur. Adhesive joints made with rubber compositions containing just 0.5 phr or more of sulfur fail by cohesive tearing within the elastomeric layer, when tested at high temperatures; the bond strength thus exceeds the cohesive strength of the elastomer. At sufficiently low temperatures, the locus of fracture changes to the interfacial region. The temperature at which this transition occurs is independent of sulfur levels, suggesting that the bond strength is not very dependent on the sulfur level, at least for concentrations in the range of 0.5–9.0 phr. Unlike NR, which generally requires 3.0 phr or more of sulfur to obtain strong bonding, CR bonds tenaciously to brass when quite low levels of sulfur are present. Additionally, an ultra accelerator such as TMTM does not “destroy” the adhesion of CR to brass, as it does in the case of NR-brass bonding. This indicates that the sulfidation reaction at the interface between the rubber and brass is highly dependent on the chemical characteristics of the elastomer and not just the nature of the compounding ingredients.
Polybutadiene Vulcanization. Chemical Structures from Sulfur-Donor Vulcanization of an Accurate Model
Authors: Gregg Earl C. , Lattimer Robert P.
Published: February 2011

Only 1,5-polyenes with three or more double bonds crosslinked in a curing recipe with 2-benzothiazolyl-N-morpholyl disulfide (BMD) or bis(dimethylthiocarbamyl) disulfide (TMTD) as the crosslinking agents. A suitable chemical model for 1,4-polybutadiene (PB) is cycIohexadeca-1,5,9,13-tetraene (CHT). The preparation of CHT is described. The crosslink density of a CHT vulcanizate agreed well with the chemical crosslink density of cis- 1,4-polybutadiene rubber, similarly cured. The crosslink density of the CHT vulcanizate was measured by isolating, identifying, and weighing the various crosslink structures. The non-crosslink structures of the network and the extranetwork structures were also identified and quantified. Various amounts of curative fragments attach to the PB network structure, as exemplified by the amount of curative fragments attached to CHT. About 16% of the lauric acid attached to the network structure. The curing agent, BMD, divided into three fragments: 2-thiobenzothiazole, morpholyl, and thio groups. About 67% of the thio groups, 25% of the 2-thiobenzothiazole groups, and about 6% of the morpholyl groups attached to the network structure. About 57% of the thio groups formed crosslinks. The main crosslink structure was 85% bis(allylic) monosulfide and 15% bis(allylic) disulfide. The length of the disulfide crosslink was only 60 pm greater than the length of the monosulfide crosslink. This compares with the 0.2 nm length of a sulfur atom. Very little cis-trans isomerization occurred in the unreacted CHT as a result of vulcanization. This indicated almost no cis-trans isomerization of unreacted segments of PB in PB vulcanizates. However, extensive cis-trans isomerization occurred in the CHT that crosslinked, which indicates that cis-trans isomerization in PB vulcanizates is confined to the reaction sites of the PB molecules. The configurational isomerism was essentially exclusively cis-to-trans. No trans-to-cis isomerism was observed. The insoluble solid in the vulcanizate was a mixture of cadmium bis(2-thiobenzothiazole), cadmium sulfide, and morpholinium sulfate. Material balances of the reaction products with the curatives showed that 90% by weight of the reaction products of the vulcanization of CHT were identified. The hydrogen transfer balance showed that CHT is the main hydrogen donor during crosslink formation. The morpholyl group from BMD was the main hydrogen acceptor and formed morpholine and morpholinium sulfate. Escape of volatile substances during vulcanization of PB resulted in much reduced crosslinking. For this reason, a hydraulic reactor for vulcanization of liquids, such as CHT, without loss of volatile substances was described.
Effects of Compound Formulation on the Adhesion of Rubber to Brass-Plated Steel Cord
Authors: Ishikawa Yasuhiro
Published: February 2011

Implications for cord adhesion from this study are as follows: 1) In the low-adhesion compounds containing low cobalt naphthenate and sulfur levels, adhesion increases with decreasing cobalt naphthenate:sulfur ratio, at a given amount of cobalt naphthenate. 2) Under mild curing condition (160°C, 20 min), high-adhesion compounds, containing high cobalt naphthenate and sulfur level, do not show a decrease in adhesion, even if the cobalt naphthenate:sulfur ratio is increased. However, after overcuring (160°C, 60 min), adhesion loss is encountered with increasing cobalt naphthenate:sulfur ratios, at a given cobalt naphthenate level. 3) A high level of unaged adhesion can be obtained if products with a combination of low cobalt and high sulfur content are formed on the brass surface. This condition obtains if the compound contains large amounts of cobalt salt and sulfur and a small ratio of cobalt salt to sulfur. 4) With a high-adhesion compound, the unaged adhesion is rather insensitive to the amount of accelerator. 5) After humidity aging, the adhesion of a high-adhesion compound varies depending upon the amounts of sulfur and accelerator. Compounds containing small amounts of sulfur show a decrease in adhesion with increasing amounts of the accelerator. However, compounds containing large amounts of sulfur maintain high adhesion, even with large amounts of accelerator. 6) For unaged adhesion, only a slight influence is observed by varying the amount of stearic acid. After humidity aging, however, compounds containing larger amounts of stearic acid show a decrease in adhesion, especially in the presence of large amounts of cobalt naphthenate. 7) Compounds which promote the formation of ZnO on the surface during bonding maintain a high adhesion level after humidity aging. This is similar to the effect of using a cord plated with brass containing a higher zinc level.
The Influence of Carbon Black, Mixing, and Compounding Variables on Dispersion
Authors: Hess W. M. , Swor R. A. , Micek E. J.
Published: February 2011

A series of response equations relating dispersion and rubber properties to mixing and compounding variables have been developed for formulations based on SBR and EPDM. These provide insight on the relationship of dispersion to rubber performance as carbon black type and loading are widely varied. Optimum conditions have been defined for minimizing Banbury mixing time and power consumption to achieve acceptable dispersion for different grades of carbon black. The different blacks can be classified in terms of their relative tendency to be shear-stress or shear-strain sensitive. The finer, low-DBPA carbon blacks such as N326 are shear-stress sensitive. To achieve high dispersion levels, this type of black requires initially high compound viscosities, i.e., by means of high loadings, withholding all or part of the extender oil until after black incorporation, or by high black/oil ratios. The coarser, high-DBPA carbon blacks such as N650 are more shear-strain dependent and will reach high dispersion levels if enough energy (usually relatively low) is imparted to the batch during Banbury mixing. N650 consistently gave high dispersion levels over a wide range of black/oil levels, regardless of the polymer type or mixing variables. Carbon black dispersibility in SBR-1500 was improved in the direction of increasing DBPA and decreasing surface area. The surface area response was most pronounced when loose oil was added with the black. High oil with the carbon black tends to form harder, more persistent agglomerates which have a greater depressing effect on rubber strength properties such as tensile and fatigue. The effect of carbon black surface area on dispersion was considerably less in SBR-1712 with no loose oil addition. In EPDM, upside-down mixes of different grades of black at varied black/oil loadings produced some notable changes in the dispersion response to carbon black DBPA. At some of the high black/oil ratios, low DBPA was actually beneficial to dispersion. The finer, higher-DBPA blacks such as N351 showed a tendency to form more persistent agglomerates analogous to conventional SBR-1500 mixes in which high amounts of loose oil are added with low-DBPA blacks. These persistent agglomerates are most prone to form in an EPDM upside-down mix when the oil loading is close to the absorptive capacity of the carbon black. The Banbury power profiles of such compounds indicated a high initial peak and a depressed or missing second peak. A normal power profile and a high level of dispersion were achieved with these problem mixes when 25 to 50% of the oil was withheld until after black incorporation. N650 gave excellent dispersion in EPDM at all black/oil loadings and only minimal variations in vulcanizate properties were observed at mixing times ranging from 1 to 5 min.
Buckling of Viscoelastic Columns. Part II: Constant Deformation Rate Buckling
Authors: Wang Shau-Chew , Meinecke Eberhard A.
Published: February 2011

The buckling of viscoelastic columns has been considered from both a theoretical and an experimental perspective. The fact that buckling occurs at relatively low strain where the SBR is nearly linearly viscoelastic allowed several simplifications in the theoretical development, leading to closed form predictions of the loading and unloading curves. This treatment neglects gravitational effects and carbon secondary structure effects and fits the experimental data best at HAF loadings around 30 phr. At lower carbon black loadings, the gravitational effects caused the experimental Euler load to be less than predicted from linear viscoelasticity theory, while at higher carbon black loadings, the carbon black structure led to higher Euler loads than predicted.
Modification of Natural Rubber Latex with Peracetic Acid
Authors: Gelling I. R.
Published: February 2011

1. The structure of the products obtained from the reaction of NR latex with peracetic acid depends on the reaction conditions. 2. Under controlled conditions, specific levels of epoxidized NR (ENR) can be obtained. A random epoxide distribution has been observed. These materials undergo strain crystallization and hence exhibit good strength properties, although at high levels of epoxidation there is a decrease in the degree of crystal-unity. Other properties, e.g., hysteresis, air permeability, and oil resistance, change systematically with the level of epoxidation. These properties indicate that ENR has the potential to become an extremely useful commercial polymer. 3. At higher acid concentrations and/or temperatures, ring opening of the epoxide groups occurs, and even low levels of ring-opened structures have been found to adversely affect the properties of ENR. 4. The nature of the ring-opened structures depends on the degree of epoxidation. At low levels of epoxidation, where the majority of epoxide groups are isolated, simple diols and hydroxyacetates are formed. However, at higher epoxide levels, where blocks of epoxide predominate, the major product is a five-membered cyclic ether. At 100 mole% modification, a white amorphous thermoplastic product was obtained consisting almost entirely of furan structures.
Anisotropy Induced in an Uncrosslinked Elastomer Via Large Strain Deformation
Authors: Hamed G. R. , Song J. H.
Published: February 2011

The anisotropy induced in an ungelled SBR elastomer upon large scale deformation and the rate at which the deformed elastomer returns to its original state upon removal of the deforming force were investigated. In these experiments, a standard birefringence technique was unsuitable for measuring the extent of orientation after release, however, tensile stress-strain measurements successfully showed the presence of anisotropy. After prestraining and then releasing, samples have an initial resistance to deformation which is the same both parallel and perpendicular to the prestraining direction. However, testpieces cut parallel with the prestraining direction show stress-strain curves that lie above those for cross-cut specimens at high elongations, while cross-cut samples have stress-strain curves remarkably similar to those of the isotropic controls. With increasing time after prestraining or for larger prestrains, the normalized anisotropy, at intermediate elongations, becomes negative; that is, in this region, it becomes easier to deform “parallel” specimens than to deform “perpendicular” specimens. This phenomenon is proposed to be the result of two opposing entanglement networks—an original one, which remains in tension, and a compressed one, which was formed by chains re-entangling while the sample was extended. Although the shapes of the “parallel” and “perpendicular” stress-strain curves may be quite different, the total energy required to rupture the samples in both cases is similar. Finally, for a lightly crosslinked sample, it is demonstrated that after various prestrains, hold times, and relaxation times before testing after prestraining, the normalized anisotropy is a unique function of the residual extension at the moment when the specimens were tested.
Pulsed and Steady Field Gradient NMR Diffusion Measurements in Polymers
Authors: von Meerwall Ernst D.
Published: February 2011

Some twenty years after the development of the steady and pulsed gradient spin-echo NMR methods of measuring self-diffusion, these techniques are now maturing and experiencing a surge of interest, much of it concentrated on polymer systems. The methods are briefly reviewed here, together with the most important results in polymers, with particular concentration on work described within the last few years. The research is divisible into three categories: diffusion of diluent and penetrant molecules in rubbery high polymers, diffusion of polymer molecules in dilute and semidilute solutions with liquid solvents, and diffusion of macromolecules dissolved in concentrated solutions or melts of equivalent or different polymers of arbitrary molecular weight. The review includes the main theoretical interpretations of the experiments, particularly the free-volume theory in its various forms and power-law behaviors postulated by recent refinements of tube/reptation and scaling theory. This article represents an updated elaboration of an earlier review.
Oxidation and Ozonation of Rubber
Authors: Keller Robert W.
Published: February 2011

With the wide variety of elastomers, fillers, and other compounding ingredients available today, there is increasing demand for rubber compounds with specific properties. The systematic development of the desired rubber compound can be undermined by the exposure of the compound to oxygen and ozone during use. Thus, a rubber compounder should be aware of the effects of oxygen and ozone attack on rubber and how to compound for oxygen and ozone resistance. This short review is intended as an introduction to the phenomena of oxidation and ozonation of rubber.
Study of the Effect of Soft-Segment Length and Concentration on Properties of Polyetherurethanes. II. The Effect on Mechanical Properties
Authors: Petrović Zoran S. , Budinski-Simendić Jaroslava
Published: February 2011

Three series of segmented polyurethanes with different soft segment lengths and concentrations were examined by TMA, DMA, and mechanical methods. Maximum tensile strengths were obtained when ssc was 40–50%, which was explained by a specific interlocking morphology. No significant effect of soft-segment chain length on maximum strength was found, but higher values were found in the C series when ssc was 60%. Elongation at break increases linearly with ssc but indications that shorter soft segments produce higher extensions was attributed to plastic flow. TMA showed that Tg was independent of ssc in the C and, to a degree, in the B series, while temperature of α-transition in DMA was independent of ssc only in the C series at ssc above 50%.
New Accelerators for Vulcanization of Rubber—Part III: Synthesis, Characterization, and Evaluation of Some 2-Mercaptobenzimidazole Derivatives
Authors: Pal D. , Khamrai A. , Adhikari B. , Dutta T. , Maiti Mrinal M. , Maiti Sukumar
Published: February 2011

Five derivatives of 2-mercaptobenzimidazole containing S—N bonds have been synthesized and evaluated for their action as accelerator-antioxidant in NR gum stocks. All these compounds exhibit varying degree of accelerating efficiency; some of them, viz. MBSTP, MBSPT, and MBDSPT, offer excellent cure characteristics and vulcanizate properties comparable to some of the best commercially available curatives such as CPTD. Substitution at the N or S atom of the MB molecule does not affect adversely its antioxidant properties; rather, an improvement in aging resistance has been achieved. The degree and nature of substitution play an important role in the antioxidation properties of these MB derivatives. Thus, disubstitution offers better antioxidation characteristics than monosubstitution, and the latter, in turn, is better than unsubstituted MB. Some discussion on correlation of reactivities of these MB derivatives and their cure synergism with CPTD have been reported. It was observed that these new accelerator—antioxidant compounds show very little cure synergism with CPTD but do show promise as dual-function curatives for natural rubber.
Natural Rubber Compounds for Truck Tires
Authors: Barnard D. , Baker C. S. L. , Wallace I. R.
Published: February 2011

An 80 NR/20 BR truck tread compound containing a semi-EV cure system and modified with a 6.0 phr level of stearic acid has been shown to exhibit excellent resistance to reversion when compared to a similar compound containing a normal 2.0 phr level of stearic acid. Improvements in the retention of laboratory abrasion resistance, heat generation, and most physical properties have been identified on test pieces subjected to typical truck retread overcure conditions. In highway fleet testing trials of 1100 × 22.5 truck retreads fitted to both third and fourth drive axles of tipper trucks, the modified compound displayed a 42% improvement in treadwear performance over the normal compound in the lower severity third axle positions while performance in the higher severity fourth axle positions was inferior by 20%. In comparison to a 55 SBR/45 BR truck tread, both NR compounds displayed superior wear performance on the fourth axles while some further adjustments of the modified compound are required to match the synthetic compound on the third axles. The reversal of wear performances for all compounds between third and fourth axles is due to the different abrasion mechanisms encountered. Laboratory abrasion rankings do not correlate with wear performances of compounds on the fourth drive axle of trucks, but they do correlate with wear performances on third drive axles. Despite the reversion characteristics of the normal semi-EV compound, no significant adverse effect on treadwear performance was evident at the start of tire life. The low heat generation of the modified compound in laboratory tests is confirmed in actual tire testing. Advantages in rolling resistance characteristics are also evident for the modified compound. Current studies at MRPRA suggest that further modifications of cure system design, in combination with the optimization of NR/BR ratios and mixing methods, will potentially provide NR dominant truck tread compounds which will exhibit superior wear performance in both the higher and lower abrasion severities encountered in heavy-duty truck tire service conditions.
Criteria for Unstable Tearing of Elastomers
Authors: Stacer R. G. , Kelley F. N.
Published: February 2011

1. Unstable, or stick-slip, tearing has been evaluated in a series of unfilled elastomers. It was found that unstable tearing in these materials occurs only in well defined regions of temperature and rate. The behavior of the material in these regions follows a definite time-dependent pattern, suggesting the existence of simple time-temperature correspondence. This has been demonstrated by showing that the same shift factors that superpose other viscoelastic functions also describe the time-dependent nature of unstable tearing. Previous work showed that the magnitude of unstable tearing could be controlled by test-specimen geometry. It is concluded in this work that the mechanistic origin of unstable tearing can be traced to viscoelastic processes of the rubbery network. The combined results of these 2 studies show that unstable tearing is a characteristic feature of the polymer network which may be controlled or eliminated by test-specimen design. 2. For the amorphous elastomers investigated, it has been shown that the boundaries between regions of stable and unstable tearing can be explained in terms of simple extension properties and characteristic viscoelastic transitions of the elastomer. Specifically, the long-time (or high-temperature) boundary between conditions of stable and unstable tearing has been associated with a critical extension ratio, λc, which corresponds to an upturn in tensile stress-strain curves. If temperature and rate conditions are such that the deforming material at the tear tip does not extend beyond λc, unstable tearing does not occur. This is consistent with an anisotropic tear-tip reinforcement model of unstable tearing which has been discussed in detail. The short-time (or low-temperature) boundary between stable and unstable tearing conditions has been related to a characteristic time, ttr, associated with the onset of the rubber-to-glass transition. This characteristic time also corresponds to a change in the simple extension response of the elastomer. At times shorter than ttr, a distinct yield point was observed in constant rate stress-strain curves. It is therefore surmised that unstable tearing does not occur in this region due to the plastic yielding of the material, which interrupts the formation of the anisotropically reinforced structure at the tear tip. 3. Time-dependent tear-energy master curves of elastomers over broad time scales all display the same general features. Near the glassy region, the elastomers were found to approach a glassy tear energy of approximately 60 kJ/m2. At much longer times, in the terminal regions of the mastercurves, the tear energy dropped rapidly. In between these two extremes, a plateau was observed for all the elastomers, with NR displaying the lowest plateau slope.
Characteristics of a Series of Energy-Absorbing Polyurethane Elastomers
Authors: Mendelsohn Morris A. , Navish Francis W. , Kim Dongsik
Published: February 2011

Compositional effects were measured on a series of polyurethanes prepared by extending MDI-terminated PTMG prepolymers with dihydric alcohols and MCHDI-terminated prepolymers with diamines. The tensile and compressive stiffness and hysteretic loss increased while the resilience decreased with a decrease in the isocyanate equivalent weight of the prepolymer. Polyol chain extenders having an aromatic structure provided greater rigidity and increase in temperature on compressive cycling than did their aliphatic counterparts. Structural linearity and symmetry of both the aliphatic and aromatic extenders promoted greater rigidity and resiliency and less damping. Although direct replacement of MDI with MCHDI gives softer polyurethanes, use of the aromatic diamine extenders with the MCHDI-terminated prepolymers gave materials displaying the least resilience and greatest rigidity under static test conditions and the highest increase in temperature on compressive cycling. However, a significant increase in the chain length of the aromatic diamine-extended prepolymer provided properties quite similar to those obtained with the aliphatic diol systems.
Corona Discharge Activation and Reconstruction of Elastomer Surfaces
Authors: Lawson David F.
Published: February 2011

Corona discharge in air appreciably increased surface energies of ethylene—propylene—diene rubber (EPDM), a blend of chlorobutyl and natural rubbers, and styrene—butadiene rubber (SBR), as determined by contact angle measurements. High energy surfaces were typically short-lived, on the order of minutes, presumably due to facile reconstruction of the surface by mobile elastomer chains. Surface activation occurred despite the relatively thick specimens (1.8–2.5 mm) and the presence of up to 35% by weight of carbon black. Electrode configurations had an effect on the experimental results. Ozone, a byproduct of corona discharge, eroded the surface of SBR. Modest improvements in the bonding of an elastomeric urethane coating were realized with some of the surface-activated elastomers.
Rubber Flow in an Internal Mixer
Authors: Griffith R. M. , Kannabiran R. , Tomlinson G. S.
Published: February 2011

A number of experimental studies have improved understanding of rubber flow in internal mixers. Freakley and Van Idris obtained flow patterns and areas of fill by photographing through a transparent end plate of a small internal mixer during rubber mixing. White and Min obtained additional information by videotaping through transparent end plates and body sides of a small internal mixer during rubber mixing. Sata and associates used observations of flow of polymer solutions in a transparent Banbury mixer to help optimize rotor design. Freakley and Van Idris, Freakley and Patel, and Toki and associates used responses from pressure sensors installed in the body of Banbury mixers to infer the fill and flow directions during rubber mixing. Here we report findings based on direct examination of the contents of a Brabender mixer removed after curing in place so as to limit further flow after stopping mixing. The technique used is basically the same as that employed in the past to determine flow patterns in screw extruders. Melotto has also used this method without curing in work to optimize mixer geometry.
An Experimental and Theoretical Study of Heat Conduction and Vulcanization of Rubber Compounds in Molds
Authors: Kong Dancheng , White James L. , Weissert Frederick C. , Nakajima Nobuyuki
Published: February 2011

A fundamental study on curing of rubber compounds in molds is presented. We have measured the thermal conductivity of a range of rubber compounds determining the influence of carbon black, other fillers, and oil. The heats of reaction associated with the curing kinetics of model compounds were measured. A mathematical model is proposed to predict the temperature profiles for curing a reactive slab. This involves inclusion of an energy generation rate, which depends on time and temperature. This is expressed through a Damkohler number. Solutions of the heat conduction equation are interpreted in terms of the Fourier number and the Damkohler number. Calculations are carried out using experimentally determined thermal conductivities and curing kinetics. Thick parts are shown to heat up more slowly (associated with the Fourier number) and to show greater overshoots of cure temperature (associated with the Damkohler number).
Relationship between Molecular Structure and Mixing Mechanism
Authors: Shiga S.
Published: February 2011

The relationship between the molecular weight, the bound rubber, and the PI value was studied for EPR, of which the molecular structure was measured with GPC-LALLS. A strong linear correlation is found between the bound rubber and the PI value. The Meissner theorem, modified to express a severer dependence of the bound rubber on the molecular weight than the original theorem expects and the use of a molecular size instead of the molecular weight, can explain the relationship between the molecular weight and the bound rubber, accordingly the PI value. They indicate not only the dependence of mixing processability on polymer adsorption, but also strongly suggest the mechanism of carbon black dispersion that aggregates are scraped out from the surface of agglomerates as illustrated by the onion model. A pulsed NMR was used to measure the spin-spin relaxation time T2 of EPR in rubber compounds of different mixing time to study the rubber phase structure and its time change. It can be imagined from the T2-time curves that till tmin, polymer molecules are rapidly bound on the carbon black surface to become thick gradually, while adsorbed segments per a molecule increase with time. After tmin, gradual rearrangement of molecules on the surface and the biphasic structure of the bound rubber may proceed. The whole thickness of the bound rubber increases gradually even after tmin. The resistance against the dispersion of carbon black seems to be strengthened with mixing time.
A Theoretical-Experimental Method for Analyzing the Dynamic Behavior of Elastomeric Lip Seals
Authors: Prati Edzeario
Published: February 2011

An analytical-experimental method has been presented, which permits the dynamic behavior of lip seals for rotating shafts to be analyzed in the presence of both interference and static and dynamic eccentricities. A mathematical model which accounts for viscoelastic and inertial effects, permits determination of the lip—shaft contact conditions, the dynamic lip profile, and the gap area for various shaft speeds. The parameters which define the mathematical model have been determined experimentally. Such a model permits the performance of the particular seal studied to be predicted for various operating conditions. Finally, the influence of parameters characterizing the viscoelastic and inertial effects on the gap area have been examined. The analytical findings correlate well with the experimental measurements of fluid leakage for practically relevant values of the shaft angular velocity.
Effect of Carbon Black on Ultimate Properties of Rubber Vulcanizates
Authors: Medalia Avrom I.
Published: February 2011

In this survey, we have concluded that carbon black reinforces ultimate properties of rubber by tear deviation. This can occur at the colloidal level, as the tear is forced to pass around carbon black aggregates, thus increasing the area of the torn surface. Colloidal tear deviation may be the cause of the increase in threshold tearing energy which appears to be a small but significant component of reinforcement. Most reinforcement under ordinary test conditions is due to macroscopic tear deviation. This appears to be caused by strands of carbon black aggregates which force the growing tear to change direction. Macroscopic tear deviation is readily observed in a trouser tear test as stick-slip or knotty tear. In the tensile strength test, tear deviation prevents catastrophic rupture until a high stress is reached. In order to be effective in this or other ultimate properties, the carbon black must not debond; i.e., failure must go through the rubber rather than through the debonded rubber—filler interface. Reinforcing carbon blacks do not debond (from diene rubbers) under normal conditions and so do not require further strengthening of the rubber—filler bonds.
Viscoelastic Response and Adhesion Properties of Highly Filled Elastomers
Authors: Stacer R. G. , Husband D. M. , Stacer H. L.
Published: February 2011

The viscoelastic response of four highly-filled elastomers has been investigated. Small deformation dynamic testing of these materials reveals thay they are nonlinear viscoelastic, as well as thermorheologically complex. Nonlinear viscoelastic behavior was observed as a pronounced strain dependence in the range of 0.1 to 10%. The degree of this nonlinear response was quantified through a constitutive equation containing a single nonlinear factor; resultant nonlinear factors for the various materials were compared and evaluated. Thermorheologically complex behavior was displayed by slightly different shift coefficients to superpose G'′ and G″ data. An approach for calculating material resilience from the viscoelastic data was also developed and a nomographic technique presented for its application. A composite adhesive joint, consisting of two layers of a filled NBR compound bonded together by a filled putty interlayer, was also studied. It was found that both the adhesive fracture energy and the effect of interlayer thickness could be related to the loss modulus of the putty interlayer. Finally, the effect of contact time on bond strength was evaluated and results presented as a master curve of adhesive fracture energy vs. temperature-reduced contact time.
Solid State Carbon-13 NMR Studies of Vulcanized Elastomers. II, Sulfur Vulcanization of Natural Rubber
Authors: Zaper A. M. , Koenig J. L.
Published: February 2011

In summary, the solid-state C-13 NMR technique has proven to be a significant method for the detection of crosslinks and other structural modifications in sulfur-vulcanized NR systems. The use of sulfur as a crosslinking agent by itself generates a considerable amount of main-chain structural modifications. Cyclic sulfide structures and cis-to-trans chain isomerization are detected in addition to polysulfidic crosslinks which are found attached to different carbons of the NR repeat unit. The phenomenon of reversion has also been detected in this study. The nature of the spectral broadening in the NMR spectra of the highly cured vulcanizates has two origins. The broadening arises from lack of molecular motion in the system and from an increase in chemical shift dispersion due to the new structures formed with crosslinking.
Thermoplastic Elastomers
Authors: Legge Norman R.
Published: February 2011

It is a great pleasure to return to Montreal to receive the Charles Goodyear Medal at this joint meeting of the American Chemical Society, Rubber Division, and the Rubber Chemistry Division, Chemical Institute of Canada. This occasion has given me a delightful opportunity to renew old friendships in both organizations and to visit again my graduate school at McGill. First of all, I thank the Awards Committee and the Executive Committee of the Rubber Division for electing me to this high honor which I share with my many collaborators who were with me during those exciting years, and with the Shell Companies. The subject of the lecture is “Thermoplastic Elastomers,” specifically the triblock copolymers based on styrene and dienes, or hydrogenated dienes. Previously I have used the subtitle, “A Successful Innovation,” where I have defined “innovation” as the successful commercialization of a new technology, process, or product. In this lecture, I shall discuss the background of the innovation, the impact of it upon the thermoplastic elastomer field, and some of the early history of thermoplastic elastomers, which I believe you will find interesting.
Magnesium Silicate Filler in Rubber Tread Compounds
Authors: Hernández Luis González , Ibarra Rueda Luis M. , Antón Celia Chamorro
Published: February 2011

The natural magnesium silicate, sepiolite (trade name Pansil), can partially substitute (up to 30%) for carbon black without important losses in physical properties and occasionally can improve them. In the NR-based compounds, as the substitution takes place, vulcanization times and Mooney viscosities decrease. Tear and abrasion resistances are lower. The same effects are observed in the SBR-based compounds, though in this case, the addition of a silane coupling agent (Silane A-189) counteracts the negative effects of the sepiolite, and the obtained values are clearly better than those with only carbon black. According to tan δ behavior in truck tire tread compounds, this filler type gives a higher wet grip resistance, but rolling resistance would be adversely affected by its use, though the presence of a silane coupling agent diminishes these effects. On the contrary, in passenger tire tread compounds, the partial substitution for carbon black seems to increase the wet resistance too, without a pronounced damage in rolling resistance. In this case, the addition of the silane coupling agent produces an increase in wet skid resistance and a decrease in rolling resistance. Based on laboratory tests, rolling resistance increases in all cases, mainly when the sepiolite was modified with silane. Wet skid resistance showed no variations. Clearly, it would be desirable to confirm our observations by an actual tire test.
Viscoelastic Properties of Nylon 6 and Nylon 66 Tire Cords: Morphological Analysis
Authors: Prevorsek D. C. , Murthy S. , Kwon Y. D.
Published: February 2011

The differences in the viscoelastic properties of conditioned nylon 6 and nylon 66 cords leading to higher shoulder temperatures of nylon 66 tires are reviewed and analyzed in terms of fiber structure. It is concluded that these differences are related to the differences in crystallographic behavior of the two polymers. The conclusions are based on the viscoelastic data from tire cords removed from tires and the properties recorded after mechanical conditioning to reach steady state equivalent to driving conditions. Viscoelastic data are obtained with the Allied high-strain viscoelastomer and structural interpretations are based on SAXS and WAXS analyses.
Techniques for Observing Microfailure in the Aramid-Adhesive-Rubber Interface
Authors: Begnoche B. C. , Keefe R. L. , Causa A. G.
Published: February 2011

A variety of techniques were developed or investigated which were useful in pinpointing microfailure locations and determining failure mechanisms at the aramid fiber-adhesive-rubber interfaces. All of the techniques were microscopy related. The scanning electron microscope was the most useful tool, especially in the seldom used backscattered electron mode, when its variety of add-on options were employed, and support techniques were developed. Optical incident-light fluorescence microscopy used in the medical field proved to be a valuable supplement to the SEM, allowing verification of the microfailure mode when used on the same samples.
Comparison of Tensile and Shear Behavior of Carbon-Black-Filled Elastomers
Authors: Nakajima N. , Scobbo J. J. , Harrell E. R.
Published: February 2011

Four NBR's and 2 SBR's with 40 phr carbon black and one SBR with 56 phr carbon black were characterized in both tensile stress-strain behavior and small-strain dynamic-shear behavior. The room temperature tensile stress-strain behavior was determined at strain rates of 0.00690, 0.0187, 0.0975, 0.0162, and 0.253 s−1. For dynamic-shear observations, loss and storage moduli were used to calculate the complex viscosity-frequency curve at small deformations and frequencies of 0.1 to 100 rad/s. Also, these data from tensile and shear experiments were compared with previous data from a capillary rheometer, high-speed tensile tester, and oscillatory tensile tester. Strain-time correspondence was found applicable to large-deformation tensile data up to the yield point. The formation of an anisotropic aggregate density in elongational deformation explains the higher viscosity and modulus for tensile behavior relative to small-strain shear behavior at similar conditions. In shear deformation and flow, the formation of an anisotropic density of aggregates does not seem to occur appreciably.
Cure Adhesion in the Interface of Fluorinated and Nitrile Rubbers
Authors: Mori Kunio
Published: February 2011

Recently there has been a great deal of interest in new composite rubbery materials. Good properties require the reinforcement of the interfacial region which is formed between different rubbers. In order to strengthen the interfacial region, it is necessary to increase the thickness of the interfacial layer and the intermolecular forces. However, in a laminate and blends of rubbers with physically and chemically different properties, it is often very difficult to obtain this as, for example, in the case of fluorinated (FR) and nitrile (NBR) rubbers. This work indicates newly developed vulcanization systems which are very effective in producing FR-NBR composite materials with very good properties, because they induce interpolymer interactions.
Dynamic Testing under Nonsinusoidal Conditions and the Consequences of Nonlinearity for Service Performance
Authors: Harris J. A.
Published: February 2011

In this work, nonlinearity in the dynamic behavior of rubber has been considered. In order to understand its effects in a service environment involving complex patterns of vibration, it has been necessary to clarify the derivations of dynamic properties for the sinusoidal excitation that is conventionally used in testing. Using the fundamental frequency components as a basis, non-linearity can be quantified by the harmonic components that it produces. A dynamic test system has been developed which incorporates the ability to perform a harmonic analysis, and the usefulness of this has been demonstrated. Harmonic analysis has enabled the dynamic behavior of rubber to be quantified under complex, periodic waveforms. This is necessary for filled rubbers, because their nonlinearity means that a superposition on their properties from sinusoidal tests is incorrect. Examples of this approach for assessing dynamic behavior range from shock mounts to tire treads. Dual-sine tests on a nonlinear rubber indicate that for complex vibrations, consisting of many amplitudes and frequencies, the overall dynamic behavior will tend toward that obtained in single sine tests at a strain amplitude which corresponds to the largest amplitude that occurs in the time history. A similar conclusion is drawn from random vibration tests with a continuous spectrum of vibrations. The result of this is that under a more complex system of vibrations, nonlinear rubbers will behave in a more linear fashion and will exhibit higher damping than indicated by their dynamic properties measured in conventional sinusoidal tests. Therefore, when the service environment of many components is taken into account, the dynamic behavior of nonlinear rubbers may give better performance characteristics than expected from conventional testing.
Microstructural Changes in the Crack Tip Region of Carbon-Black-Filled Natural Rubber
Authors: Lee D. J. , Donovan J. A.
Published: February 2011

CB facilitates strain-induced crystallization and increases the size of the crystallized zone at the stressed crack tip. Both effects are major reinforcement mechanisms that increase the fracture resistance of CB-reinforced NR.
Strain Amplification of Elastomers Filled with Carbon Black in Tensile Deformation
Authors: Nakajima N. , Scobbo J. J.
Published: February 2011

This work is based on data previously obtained by the tensile stress-strain and dynamic-shear measurements with several gum rubbers and carbon-black-filled compounds. The gum rubbers were three NBR's of different molecular architecture and two SBR's, one of which was oil extended. The compounds contained 40 phr of N550 carbon black. Through the data treatment procedure developed in this work, the strain amplifications in the dynamic shear and tensile stress-strain measurements were evaluated with the uncrosslinked compounds. Each compound showed a unique pattern of strain amplification.
Stabilized Curative Blends for Rubber
Authors: Sommer J. G.
Published: February 2011

Blending of curatives offers several advantages. These include a sharply reduced number of weighings of curative ingredients, reduced weighing costs, reduced dusting and improved cleanliness. These advantages might not be realized with some curative blends. For example, diphenyl guanidine (DPG) could not be blended with sulfenamide accelerators because it reacted chemically with the sulfenamides. Later work assessed the effect of 2-mercaptobenzothiazole (MBT), sulfur (S), or free amine on the hydrolytic stability of N-cyclohexyl-2-benzothiazyl-sulfenamide (CBS) that was highly purified. Results showed that free amine or sulfur accelerate the hydrolysis, but to a lesser extent than MBT. The present work shows that aging of curative blends (like S, CBS, and DPG) sharply reduces the scorch resistance of rubber compounds containing the aged blends. Selected additives will stabilize the blends.