bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyisocyanates as Curing Adjuvants for Ethylene—Propylene Terpolymers
Authors: Wolfee J. R. , Albin J. R.
Published: February 2011

Ethylene—propylene—nonconjugated diene terpolymers yield vulcanizates of high modulus and tensile strength in the presence of strongly reinforcing fillers. In many applications where low cost, light color, or nonconductivity are required, it is necessary to use poorly reinforcing mineral fillers. The combination of poorly reinforcing mineral filler and amorphous EP terpolymer yields vulcanizates which do not have the excellent stress-strain properties characteristic of many black loaded stocks. The purpose of this paper is to present a new method of obtaining superior properties in mineral filled EP terpolymer vulcanizates.
The Analysis of Antioxidants and Accelerators in Rubber Compounds and Vulcanizates
Authors: Auler H.
Published: February 2011

In the rubber industry the number of accelerators and antioxidants has increased greatly in the last few years. Van Alphen even in 1956 described 154 accelerators and 87 antioxidants of different chemical structure. The detection of such a large number of materials, depending on their combination in stocks, is more or less difficult, although the detection of the presence of one or another compound often makes possible a prejudgment as to which other substances can be counted on and which cannot. Besides the chemically homogeneous accelerators and antioxidants, use is also made of mixtures as combination products. The individual components are qualitatively detectable in mixtures. Information on the type of these products is given by quantitative determination methods such as described by Zijp, Kortum, Szalai and Szöke, among others. The original substances are often chemically altered during vulcanization or later in the preparation of samples for testing; e.g., symmetrically constituted disubstitution products may split into monomers, substituents split off from the basic molecule, or reactions of various types take place which render the investigation difficult. The identification of antioxidants and accelerators received a great impetus from the application of chromatography which is of importance today as a method of separating the individual materials for subsequent physical determination methods. After Tswett has recognized decades ago the separating effect of absorption columns in the analysis of compounds of chemically similar structure, this method was used only much later for the Chromatographic investigation of rubber compounds. The earlier analytical methods in this field depend on the use of conventional methods, e.g., selective extractions and precipitation of the substances to be isolated, which are then identified in pure form by melting point determination.
Effects of Self-Diffusion and Inter-Diffusion in Polymer Systems
Authors: Voyutskii S. S. , Vakula V. L.
Published: February 2011

Diffusion of low-molecular substances in high polymers has been the object of study by many Soviet and other investigators during the past two decades. Included is the work of Reitlinger, Zhurkova, Ryskin, Malinskii, and Vasenin in the Soviet Union, and Barrer, Crank, Long, Auerbach, van Amerongen, McCall, Shtamm, and many other authors elsewhere. By way of contrast, the effects of self-diffusion in polymers and diffusion of polymer in polymer (inter-diffusion) have been given little study because of the great experimental difficulties and the complexity of theoretical explanations. Meanwhile, these effects have considerable scientific and practical significance. As will be seen hereafter, very many properties of polymers are associated in some manner with diffusivity of macromolecules or their segments. No less important is the tendency toward self- and inter-diffusion of polymers in processing and use. The aim of this review is to correlate data concerning self- and inter-diffusion of polymers containing elastic molecules (elastomers), available in several studies, and to suggest further paths for investigation of this problem.
Tack in Rubber
Authors: Bussemaker O. K. F.
Published: February 2011

The expressions tack, tackiness, and stickiness have been in use since the beginning of the rubber industry. During the years their meaning has changed considerably. The first occasion where tackiness was mentioned was in the case of crude natural rubber. The surface of the rubber became tacky or sticky during storage. This phenomenon has been thoroughly discussed in the literature. As a general conclusion it was accepted that both oxidation and depolymerisation occurred. Three factors were reported to be the cause of these processes: light, traces of copper, and manganese. From our point of view we would call this effect stickiness, as we are only interested in the building tack of rubber. In the period when the only rubber was natural rubber and high loadings of highly active fillers were not generally used in compounds, building tack was no problem. Building tack was first mentioned in a publication by Griffith and Jones in 1928. They started their experiments by measuring tack in their search for methods to prevent cotton liners from sticking to unvulcanized rubber. One would have expected much work on the measurement and improvement of tack in Germany and Russia during the development of synthetic rubbers. However, this only proved to be the case in Russia. The first publication available was the translation of an article by Voyutskii and Margolina in 1957. From Voyutskii's work we were able to trace the first article in 1935 by Zhukov and Talmud, who studied the adhesive power of synthetic rubber. In the USA the first theoretical approach to the subject was by Josefowitz and Mark in 1942, who at that time did not realize the difference between stickiness and tack. This difference became clear when lack of tack became the big problem in the use of synthetic rubber. In many cases it was found that addition of resins and softeners gave a very sticky compound which had no building tack at all. The tack problem was first discussed at the ASTM symposium on the application of synthetic rubbers in 1944 by Juve who gave a definition of building tack. From that time, the problem has been studied regularly, especially from the practical side, to find ways and means to improve the building tack of synthetic rubbers.
Characterization of Viscoelastic Behavior of Stereoregular Poly(Isoprenes) by Relaxation Experiments
Authors: Szilagyi L. , Riccò T. , Danusso F.
Published: February 2011

The mechanical relaxation of twelve samples of unvulcanized cis poly-(isoprene)s, including both natural and synthetic polymers, was studied over a range of temperatures. Master curves of relaxation modulus obtained from these data were used to derive relaxation spectra according to linear viscoelastic theory. A recent theory was used to calculate mean values of quantities related to the supermolecular structure which occurs spontaneously in these materials and is responsible for their viscoelastic properties. This structure is schematized in a model consisting of a system of macromolecules which interact with each other by elastic forces and frictions corresponding to points of entanglement between chains. The analysis leads to the determination, for each sample, of the number of entanglements per molecule, the physical network density, the value of relaxation parameters, and the relationship of each of these quantities to molecular weight.
New Methods for Electron Microscopy of Polymer Blends
Authors: Smith R. W. , Andries J. C.
Published: February 2011

Two new methods of sample preparation have been developed for electron microscopical examination of polymer blends. The first is an ebonite method where the blend is hardened in a sulfur-sulfenamide-zinc stearate mixture and then microtomed. The second is a cryogenic method where the blend is microtomed in the frozen state and then stained with osmium tetroxide. These methods have been used to examine styrene—butadiene rubber/cispoly (butadiene), natural rubber/ethylene propylene diene monomer rubber, NR/trans Polypentenamer blends, and a NR/starch mixture. Sharp, clear phase differentiation is obtained with all blends studied. SBR/PB blends were obtained when the viscosities of the blended polymers were similar. Similarity of molecular structure, increased milling time, and increased milling temperature also decreased the zone size of the dispersed phase. A three-phase system was observed when a high-styrene SBR was blended with PB ; the third phase consists of block poly (styrene) embedded in the SBR phase. Under all conditions SBR/PB blends were found to be heterogeneous, with no evidence of a single homogeneous phase.
New Types of Premature Vulcanization Inhibitors
Authors: Hopper R. J.
Published: February 2011

The activity of the thiosulfonamides and dithiotrichloromethanes as retarders is apparently a result of their ability to function as BTSH trapping agents. The effect of substituents on retarder efficiencies seems consistent with a mechanism involving a three-way competition between crosslinking, retardation, and decomposition of retarder to non-functional products. The key reaction responsible for trapping BTSH probably involves a nucleophilic displacement. Substituents which favor this type of displacement increase efficiency when they are on the portion of the retarder molecule which combines with BTSH; when they are on the portion which becomes the leaving group, they evidently promote decomposition, causing a net decrease in retarder efficiency.
Studies on MBT-Accelerated Sulfur Vulcanization of Natural Rubber Reinforced with Carbon Black
Authors: Bhoumick S. , Banerjee S.
Published: February 2011

Studies have been made on the mechanism of MBT accelerated sulfur vulcanization of natural rubber containing semi-reinforcing carbon black as a filler. DCP has been used as an aid to distinguish between free radical and polar mechanism. Results indicate that sulfuration by MBT and sulfur proceed by a free radical mechanism but it becomes polar when ZnO and stearic acid are also present. Carbon black does not interfere in the sulfuration but it gives rise to additional crosslinks.
Studies on Dicumyl Peroxide Vulcanization of Styrene—Butadiene Rubber in Presence of Sulfur and 2-Mercaptobenzothiazole
Authors: Das C. K. , Banerjee S.
Published: February 2011

The effect of sulfur, MBT, zinc oxide, and stearic acid on the DCP vulcanization of SBR has been studied. DCP decomposition obeys first order kinetics in all cases, but its rate constant is higher in presence of MBT. Sulfur and MBT reduce the crosslink density due to DCP. In the mixes containing sulfur, MBT, zinc oxide, and stearic acid in presence of DCP the crosslink density is initially additive. Here oxidation of some pendent vinyl groups are effected by DCP, and these groups also take part in thiol addition reaction with MBT. The thiazole accelerated sulfuration of SBR proceeds fundamentally by the same mechanism as reported for NR, but the details show slight difference chiefly due to the presence of pendent vinyl groups and styrene units in the chain and due to the absence of pendent methyl groups in SBR.
Radiation Chemical Conversions in Fluorine Containing Elastomers under Different γ-Irradiation Conditions
Authors: Kryukova A. B. , Kuz'minskii A. S. , Gilinskaya N. S. , Galil-Ogly F. A. , Sankina G. A.
Published: February 2011

Rates of radiation chemical crosslinking and scission of fluorine containing elastomers based on copolymers of vinylidene fluoride with trifluorochloroethylene (Copolymer 1), with hexafluoropropylene (Copolymer 2), and with a perfluoroalkyl vinyl ether (Copolymer 3) and also the behavior of their radiation vulcanizates in the stressed state at high temperatures are determined both by the type of polymer and by the irradiation conditions. Crosslinking rates of Copolymers 2 and 3 are higher than those of Copolymer 1; oxygen of the air inhibits crosslinking by γ-radiation; by irradiation in the presence of oxygen of the air, the sol fraction is 8–10 times higher than in its absence, Copolymer 3 vulcanizates obtained by irradiation in the absence of air appear to be optimal.
Dependence of the Polymer-Solvent Interaction Parameter of Vulcanizates Based on Cis-1,4-Poly(Butadiene) on the Type and Concentration of Vulcanizing Agent
Authors: Gavrilov V. M. , Shvarts A. G.
Published: February 2011

Values of the polymer-solvent interaction parameter were obtained for cis-1,4-poly(butadiene) vulcanized with alkylphenol—formaldehyde oligomer, sulfur, and peroxide systems swollen with heptane, benzene, and m-xylene. The dependence of the interaction parameter on the degree of crosslinking was demonstrated. The method of vulcanization does not affect the dependence of χ on υr for good solvents, but influences this dependence for n-heptane, a weak solvent. It was shown that the better the solvent, the stronger the dependence of the interaction parameter on the degree of crosslinking.
Force—Deflection Relations for a Model Air Spring
Authors: Gent A. N. , Thomas A. G.
Published: February 2011

Force—deflection relations are derived for a model air spring consisting of two long rigid plates connected at their edges by flexible membranes and containing air under pressure. Compressive, tilting, and shear deflections are considered. Compressive forces are evaluated for three representative conditions: an isolated spring; one connected to an auxiliary reservoir of equal volume; and one with the internal pressure maintained constant. Corresponding membrane tensions and elongations are calculated. Tilting and shear load-deformation relations are specialized to the case of small deflections in order to deduce the corresponding stiffnesses. Compression of a relatively thin circular air spring is also treated. Attention is drawn to a number of potential instabilities.
Filler Aggregates and Their Effect on Reinforcement
Authors: Medalia A. I.
Published: February 2011

The most highly reinforcing fillers, namely carbon blacks and silicas, consist of aggregates of quasi-spherical particles fused together. In the absence of direct experimental studies with single-particle carbon blacks or silicas of high surface area, we cannot be sure if aggregated structure is essential for good reinforcement, or whether aggregation and fusion just happen to accompany the formation of fine particles at practical concentrations. In any case, there is no doubt that the aggregate nature of the filler plays a major role in determining the properties of the rubber compound. Here I would like to review what we know about filler aggregates, especially of carbon black, and suggest some mechanisms for their effects on rubber; and also indicate where our knowledge seems inadequate at the present time.
Tire Cord Dip Pick Up by Atomic Absorption Spectroscopy
Authors: Firkins J. L.
Published: February 2011

Graphite furnace atomic absorption spectroscopy has been used to develop a quick and accurate test for tire cord dip pick up. Strontium nitrate solution is added to either predips or resorcinol-formaldehyde latex dips at predetermined levels of a few parts per million. Sufficient replicate analyses of one to three milligram samples of treated cord can be run to provide reliable data on both the absolute level of dip pick up and the short term uniformity of the dip. The technique offers substantial advantages in both turn-around time and total analysis time relative to wet gravimetric techniques in current use.
Particle Size Determination of Tire-Tread Rubber in Atmospheric Dusts
Authors: Cardina J. A.
Published: February 2011

Ambient dust was sampled with an Andersen high volume sizing impactor within twenty feet of heavy traffic on the Akron expressway and analyzed for tread rubber by pyrolysis gas chromatography. Methods were developed for removing dust particles from the collection surface and preparing them for pyrolysis. Those particles which lie in the respirable range 1.1 to 7.0 microns constitute 25 to 40 per cent of the total by weight. The remainder is divided about equally between the size range above 7.0 microns (not respirable) and those below 1.1 microns, i.e., about one-third of the dust lies in each size category. The amount of tread rubber in these respirable dusts as determined by styrene, dipentene, and vinylcyclohexene in their pyrolyzates varied from 1.5 to 9.2 per cent with an overall average of 4.3 per cent. In the size range above 7.0 microns a high value of 13.1 per cent rubber was found with an average of 6.3 per cent. In terms of micrograms per cubic meter of suspended particulates in the respirable range 1.1 to 7.0 microns, the values for tread rubber ranged from 1.0 to 4.9 with an average of 2.6. The low potential for health hazards from this respirable dust can be appreciated from a comparison with safe levels (TLV's) for certain pollutants known to be highly toxic as follows: Beryllium—2, lead compounds—150, mercury alkyls—10, cristobalite—50.
Dynamic Mechanical and Electrical Properties of Vulcanizates at Elongations up to Sample Rupture
Authors: Voet A. , Morawski J. C.
Published: February 2011

Dynamic properties of vulcanizates have been measured at small and large extensions, up to specimen rupture, by means of a modified Rheovibron. The influence of temperature, frequency, and amplitude on the dynamic moduli has been determined for a number of SBR samples, uncharged or charged with silica or carbon black. A study has been made of the dynamic Mullins effect (stress-softening) and of dynamic stress-relaxation for various charged and uncharged samples. Electrical conductivity has been determined simultaneously with dynamic properties for carbon-black loaded elastomers. The gradual reformation of a previously destroyed secondary filler network could be followed quantitatively in rate and magnitude at very low frequencies. It appears that at small deformations a secondary, reversible filler network plays an important part in the dynamic properties of the vulcanizates. At intermediate deformations, however, this network has been eliminated. Conductance data of carbon-black loaded vulcanizates indicate a phenomenon of orientation of anisometric aggregates. At still higher deformations irreversible changes are observed, pointing to a rupture in filler—elastomer bonds as well as of elastomer chains, two experimentally distinguishable phenomena.
Raman Spectral Studies of 2-Mercaptobenzothiazole Accelerator Systems
Authors: Kapur R. S. , Koenig J. L. , Shelton J. R.
Published: February 2011

A mechanism for the formation of the rubber-bound intermediate in the vulcanization of elastomers has been proposed. The active sulfurating agent is a polysulfide. Laser Raman spectroscopy has been used to provide significant evidence for this mechanism in the presence of cis-1,4-poly(butadiene).
Radiation Curing of Ethylene—Propylene—Diene Elastomers
Authors: Eldred R. J.
Published: February 2011

A significant reduction of the radiation dose required to cure EPDM elastomers can be obtained by introducing crosslinking monomers into the compounds. Multifunctional acrylates are more efficient than either allylic or pendent-vinyl crosslinking agents. The curing rate is also affected by the nature of the unsaturation in the base polymer. Compounds of EPDM containing 5-ethylidene-2-norbornene are more reactive than those with 1,4-hexadiene. Increasing polymer unsaturation levels above 3 per cent or changes in ethylene—propylene ratios have little effect. Curing rate is dependent, however, on the Mooney viscosity of the elastomer, with higher viscosities yielding faster cures. The addition of extender oils drastically reduces radiation efficiency, which depends on both the nature and the level of the oil. This can be overcome by increasing the monomer content. The physical properties of radiation-cured EPDM compare favorably with those of sulfur-cured EPDM. The radiation-cured EPDM exhibits greatly improved compression set and oil resistance.
The Effect of Structure Breakdown of Carbon Black on Rubber Properties
Authors: Boonstra B. B. , Dannenberg E. M. , Heckman F. A.
Published: February 2011

Mechanical processing of carbon blacks by a novel pressure-milling technique provides a controlled breakdown of primary carbon-black aggregates. In contrast, direct compression has a much smaller effect on aggregate size. In rubber vulcanizates, the pressure-milled carbon blacks give about the same vulcanizate properties as normal carbon blacks with the same void volume or DBP absorption value. Breakdown of aggregates occurs during the process of incorporating and dispersing carbon black in rubber. The retention of average aggregate size after mixing in rubber is in the range of 60–70 per cent for Vulcan M (N339), a new technology tread black. We have shown that the DBP absorption method cannot distinguish between loss in void volume by compaction of aggregates versus the actual breakdown of aggregates. The sedimentation method by centrifuging provides a means for measuring aggregate size independent of the original packing of the dry black. In order to carry out these studies, a number of new experimental techniques were used. These include: a) controlled aggregate size breakdown by pressure-milling. b) Stokes diameter distribution measurements by centrifuging aqueous dispersions in a Joyce Loebl apparatus. c) Quantimet analysis of projected aggregate areas from electron micrographs from specially prepared solvent dispersions of rubber-carbon black samples where the aggregates are clear of interference from adhering rubber. It has been shown for the first time that for both Vulcan M (N339) and Vulcan 6 (N220) the median Stokes diameters, DSt, obtained by the centrifuge method and the equivalent sphere diameter, De, from Quantimet projected image analysis are in the range of 123–153.
Spin-Label Investigation of Polyurethane Networks
Authors: Ward T. C. , Books J. T.
Published: February 2011

Two types of polyurethane networks were examined using the spin-label technique. Nitroxide free radicals which are stable under moderate conditions were covalently attached to the network chains of amorphous polymers based on (1) poly(tetramethylene glycol), p,p′-diphenylmethane diisocyanate (MDI), trimethylolpropane, and (2) ethylene glycol, MDI, glycerine. Polymer (1) had very low “hard block” content, polymer (2) a very high content. Mechanical properties and differential thermal analysis measurements were made on polymer (1). Electron spin resonance spectra of the samples were obtained in the unstrained, strained, and swollen states. Large differences in the spectra were observed, depending on chemical composition, temperature, and state of swelling. Transitions from “frozen” to “rapid motion” type of spectra occurred at 70° for polymer (1), at −10° for polymer (1) swollen to equilibrium, and were unobserved up to 150° for polymer (2). Since the nitroxide label was necessarily adjacent to MDI units, was present in very small concentrations, and experienced no alterations in environment as “soft segments” did, then it is suggested that the spin-label technique is a valuable tool for analyzing microstructure of pseudoamorphous systems.
Uranium Catalysts for the Synthesis of Highly Cis-Tactic Polydienes
Authors: Bruzzone M. , Mazzei A. , Giuliani G.
Published: February 2011

Among the several transition metals used for the synthesis of polymers by Ziegler-Natta catalysts very little attention has been devoted to uranium, notwithstanding the undoubted interest that this metal offers from both the scientific and economical point of view. In fact, uranium gives the organo-metallic and the polymer chemist wide possibilities of synthesis, owing to its manifold coordination possibilities. From the economical point of view, uranium is already a cheap material, as a byproduct of nuclear fuel cycles, and one can easily foresee that, as happened in the past for coal and crude oil, uranium will have a future as a raw material in addition to its use as an energy source. The large potential supply of depleted uranium from the existing gaseous diffusion plants in the world and a forecast of this supply in western Europe from 1975 to 1985 is reported in Table I. This forecast is likely to be underestimated as it was made before the present worldwide energy crisis.
A Comparison of Tensile Stress-Strain Data from Dumbbell, Ring, and Oval Specimens
Authors: Myers F. S. , Wenrick J. D.
Published: February 2011

Our study has shown that the tensile bar or dumbbell gives higher values for failure stress and strain than does either the ring or oval specimen. This should be expected since the tensile bar permits a primarily uniaxial test and one without the stress-concentrating pins used for the ring and oval. However, it is very difficult to obtain accurate low-strain data with the tensile bar. Also, the strain rate is not constant because of tab deformation. The ring, oval, and tensile bar show agreement for values of stress and strain above 100 per cent strain but below failure. For soft, low modulus stocks the ring and oval agree at low strains. For stock with tensile modulus values above 1000 psi, the bending stress and strain, required to straighten the ring to its in-test configuration, significantly affect the data. There is less ambiguity in reducing the data from tests run with the oval than from those run with the ring, whether reduction is done manually or through direct acquisition by computer. This is again because of the initial straightening of the ring. For both the ring and oval, the material in contact with the pin experiences non-uniaxial deformation and becomes the site of failure. Yielding, as defined in this paper, can be related to hysteresis effects and hence to the phenomenon known as cyclic softening. The stress at 300 per cent strain and the stress and strain at failure are not sufficient to characterize stress-strain behavior, particularly for thermoplastic elastomers.
Stress-Strain and Stress-Birefringence Studies on Natural Rubber, Isomerized Natural Rubber, and Synthetic Poly(Isoprene)
Authors: Mukherjee D. P.
Published: February 2011

With respect to stress-birefringence, isomerized natural rubber behaves the same as natural rubber at low elongations, but at high elongation levels the natural rubber sample exhibits higher stress-hysteresis accompanied by higher mechanical loss energy. Therefore, it appears that at low elongation level the viscoelastic rate process governing the stress-strain hysteresis is not sensitive to structural imperfection (within the range of cis-1,4 content studied here), but the crystallization process at higher elongation is strongly dependent on the cis content. This is in agreement with the conclusion made by Scott and co-workers from their dynamic measurements on synthetic poly(isoprene)s. The difference in cis-content between Natsyn and natural rubber and the effect on crystallizability explains the lower hysteresis on the stress-birefringence plot for Natsyn. Similar reasoning explains the stress-birefringence difference between the A.C. rubber and Natsyn. The data, however, shows that Natsyn has the lowest amount of loss energy of the three samples (except at very high input energy >4.5). This difference might be due to effects of physical entanglements or gels which may differ. In addition, the difference in microstructure contributes to the difference in extent of strain-induced crystallization. Since the viscoelastic rate process governing the stress-strain behavior and the strain-induced crystallization are associated with molecular motion, they may not be independent.
Stress Relaxation of SBR Vulcanizates with Various Crosslinking and Modifying Agents
Authors: Vasilev A. , Dorosieva V.
Published: February 2011

From the results of the investigation on stress relaxation in air of vulcanizates based on SBR containing ε-caprolactam and alkylated phenol formaldehyde oligomer, the following conclusions can be made : 1. ε-caprolactam has an effective action as an accelerating and modifying agent leading to vulcanizates of improved behavior in stress relaxation at temperatures up to 120°C. The characteristics of the vulcanizates deteriorate at higher temperatures because of the strong temperature dependence of the rate constants of thermo-oxidative aging processes. 2. ε-caprolactam in combinations with Vulkacit CZ or Captax added in recipes of SBR leads to improved relaxation properties of the vulcanizates at low temperatures and to a lower resistance to aging at higher temperatures. 3. The vulcanizate containing the crosslinking and modifying group of alkylated phenol formaldehyde oligomer with ε-caprolactam is characterized by its highest thermostability at high temperatures in comparison with all tested compositions, and by relaxation properties at low temperatures comparable to those of the compound with Captax (Table II). 4. The relaxation curves are comparatively well described by the Berry equation for simultaneous occurrence of breakdown processes for several kinds of crosslinks by first-order reaction. 5. The slow stage of physical relaxation is described by a sum of several exponential processes with relaxation times characteristic of each composition, i.e., the various accelerators and modifying additives have a strong effect on the supermolecular arrangement of the network of vulcanizates made of SBR (Bulex).
Airborne Particulate Debris from Rubber Tires
Authors: Pierson W. R. , Brachaczek Wanda W.
Published: February 2011

Airborne particulate matter worn from tires has been detected in the atmospheres of two vehicle tunnels and in the open air. The amount is about 20 per cent as great as that from vehicle exhausts, and represents a small fraction of the tread material that wears from tires. Tread rubber was found on tunnel walls and in roadside dust, dustfall, and topsoil. A material balance shows that most of the material lost by tires in service is particulate matter, of which only a small fraction is airborne.
Friction between Conical and Spherical Shaped Sliders and Wet Rubber
Authors: Sabey B. E.
Published: February 2011

Investigations have shown that a high skidding resistance on wet roads is associated with the presence of sharp edges in the road surface: on these sharp edges high pressures are set up which assist in breaking through the lubricating water film between tire and road. This paper gives some details of laboratory tests now being made to investigate further the dependence of skidding resistance on such localized pressures. Pressure distributions beneath rigid spheres and cones pressed into rubber have been calculated, on the basis of the elastic theory, from measurements of their penetration into tire-tread rubber under load. The experimental evidence confirms that under the conditions of test employed the rubber is behaving as an elastic material. The effect of the pressures on friction under wet conditions has been investigated by sliding different shapes over wet rubber, using a laboratory friction machine designed to simulate conditions between tire and road when skidding takes place. These tests indicate that the coefficient of friction recorded under wet conditions is closely related to the pressure over the contact area between slider and rubber, and that, to ensure a satisfactory skidding resistance in wet weather, the shape of individual projections in the road must be such that average pressures of the order of 1000 lb in−2 are set up on them. Ideally, what is required is that the individual projections in the surface of the road should have angles at their tips of 90° or less : the necessary pressures are unlikely to be obtained with rounded or polished projections, whatever their size or the load applied to them.
The Friction of Hard Sliders on Lubricated Rubber: The Importance of Deformation Losses
Authors: Greenwood J. A. , Tabor D.
Published: February 2011

A study has been made of the friction of hard spheres and cones on a well lubricated rubber surface under conditions where relatively large deformations are produced. It is found that with spheres the sliding friction is almost the same as the rolling friction. Earlier work has shown that in the latter case the friction arises primarily from hysteresis losses in the rubber and it is concluded that, under the experimental conditions described, the main source of friction in lubricated sliding arises from the same cause. With conical sliders it is not possible to make a direct comparison with rolling experiments, but a simple calculation suggests that here again the friction is largely due to deformation losses in the rubber. For cones of small semi-angle there is a large increase in friction but this is associated with penetration of the lubricant film and tearing of the rubber. The friction results are in close agreement with measurements described by Miss Sabey for spheres and cones sliding on wet rubber at relatively high speeds (c. 6 ft sec−1). This suggests that in her experiments the water film provides very effective lubrication and that the friction arises largely from hysteresis losses in the rubber itself. As a general conclusion this study of the friction of lubricated rubber suggests that where interfacial adhesion is small and where relatively large local deformations occur the friction may well be dominated by deformation losses in the rubber. Under these conditions we may therefore expect the friction of hard spherical or conical sliders on rubber to be greater for rubbers of low Young's modulus and high hysteresis losses.
Hysteresis Losses in the Friction of Lubricated Rubber
Authors: Tabor David
Published: February 2011

The main point brought out in this paper is that when well lubricated rubber surfaces slide over hard protuberances the major part of the resistance to sliding may well arise from hysteretic losses in the rubber itself. Any factor, such as temperature or frequency of deformation, which affects the hysteresis losses will have a corresponding effect on the friction. This suggests that the resistance to sliding on wet or slippery road surfaces may be considerably increased by using a tire rubber which maintains a high hysteretic loss over the range of speeds and temperatures developed during operation. In order to reduce the tendency to overheat a duplex structure is suggested in which the body of the tire has low losses whilst the tread has high losses. The free rolling friction of the tire may be kept low both by modifying the geometry of the tire to give a long narrow band of contact with the road surface, and by using fine texture protuberances on the roadway. The author is aware of the fact that he has drawn rather far-reaching practical conclusions from simple laboratory experiments; nevertheless there is an increasing body of evidence supporting the view that the idea of hysteretic losses is an important one in enabling us to understand and indeed to control the friction of rubber on slippery surfaces. It should be possible, perhaps by working on these lines for the tire manufacturer and the highway engineer, starting from fundamental principles, to produce a combination of tire properties and highway characteristics that will ensure a greater measure of skid resistance on wet or greasy roadways.
Estimation of State of Cure with S-35
Authors: Pederson H. L.
Published: February 2011

The use of S-35 in a vulcanizate can lead to an easy determination of bound sulfur as the ratio of activities of the acetone extracted sample and the same sample in its original state. At present, we do not specify the meaning of the sulfur value determined in this manner otherwise than that it is a gross value ideally free from accelerator sulfur. A number of Russian papers have reported the use of radiosulfur in vulcanization studies—for instance, Blokh's survey. Later Dogadkin described exchange reactions specifying the character of the sulfur bond in combination with an extensive discussion of the chain mechanism for the function especially of thiurams, leading to at least three types of vulcanizates: nonsulfur thiuram cures with —C—C— crosslinks and no exchange at all, DPG stocks having a high exchange rate, and thiazole mixes having intermediate rates. Of course, this is a very general picture explaining only the outstanding differences in aging stabilities imported in the systems mentioned. The quoted papers give very little experimental detail. However, there is a description of the exchange that can be performed by boiling the sample in a benzene solution of the reactant—e.g., sulfur or accelerator. It is of minor importance where the radioactivity is placed; however, the treatment of inactive vulcanizates with solutions of active material is very unpleasant. Therefore the active material is added in every case by compounding and the exchange is carried out by means of an inactive solution in acetone. The present work was undertaken to investigate differences in stability of the sulfur bond in vulcanizates having increasing states of cure, preferentially in a series of vulcanizations at constant temperature. In addition to exchange with elemental sulfur and sulfur donors (tetramethylthiuramdisulfide) we have investigated the Meyer and Hohemenser reaction with methyl iodide, more elaborately developed by the brilliant work of Selker and Kemp. This reaction is thought specifically to indicate the allylic bound sulfur. It is easily performed by boiling the active vulcanizate with a mixture of methyl iodide and acetone. Fletcher and Fogg indicate in their recent work that thiuram-sulfur systems owe their remarkable aging resistance to the content of ZnDC formed by the decomposition of thiuram during cure. Further, it is well known that certain compounds, such as the zinc salt of MBT, give a similar improvement. We therefore stress that stabilities as stated here, based upon the exchange reaction, will not necessarily bear a unique relation to aging stability, but rather show an intrinsic stability of the sulfur bond.
The Low Temperature Properties of Natural Rubber as Affected by Reaction with Thiol Acids
Authors: Ritter F. J.
Published: February 2011

It has been demonstrated that the tendency of natural rubber to crystallize at low temperatures can be considerably reduced by the reaction of natural rubber with relatively small quantities of a thiol acid of the RCOSH type. Most thiol acids react already at room temperature with natural rubber. The reaction is very easy to carry out. A simple admixture with dry natural rubber, e.g., on a mixing mill or in an internal mixer, is sufficient. The reaction can also be carried out in solution or in latex. If amounts of thiol acids are used which do not exceed 1 mole %, pure gum vulcanizates can be obtained which show a strongly reduced tendency to crystallize and which nevertheless show a tensile strength of more than 150 kg/cm2. This may be explained by the fact that these rubbers still show appreciable crystallization upon stretching to elongation approaching the elongation at break, as indicated by the x-ray diffraction patterns of the stretched vulcanizates. If the thiol acid rubber vulcanizates are reinforced with carbon blacks, the tensile and tear strengths are much improved. Vulcanizates with very satisfactory room temperature properties are thus obtained, whilst the improved resistance to crystallization is retained, The abrasion resistance and the aging resistance are at least as good as those of comparable vulcanizates of unmodified natural rubber. If low temperature plasticizers are mixed into thiol acid rubbers, the glass point of the vulcanizates can be strongly reduced. TR 10 values as low as −80° C in pure gum vulcanizates and −69° C in carbon-loaded vulcanizates have been obtained. These rubbers, moreover, did not show any crystallization at low temperatures.
Infrared Spectroscopy in the Study of Reactions between Rubber and Sulfur
Authors: Klauzen N. A. , Dogadkin B. A.
Published: February 2011

There is a considerable amount of literature on the subject of the quantitative determination of the content of 1,4- and 1,2-diene units in polymers with the help of infrared absorption spectra. A similar type of investigation is conducted with dilute solutions of pure polymers. As standards these investigations utilize low molecular weight hydrocarbons which simulate 1,4- and 1,2-diene units in rubbers. However, up until recently there have been no reports on spectra investigation of the changes in the unsaturation of rubber produced during its interaction with sulfur or other vulcanizing agents. The difficulty with such type of investigation is fundamentally associated with the decrease of the solubility of rubber during vulcanization. Vulcanization in solution gives systems which are transparent to infrared rays but is complicated by the fact that the solvents transparent in the region of 10– 12 microns (CCl4 and CS2) have low boiling points. Nor is there excluded the possibility of interaction of rubber with solvent at vulcanizing temperatures. The present work presents a method for determining unsaturation in films of vulcanized rubber. The investigation was conducted with a spectrograph ISP-14(b) with a sodium chloride prism. For analysis use was made of absorption at 10.3 microns for trans-1,4-units and at 11 microns for 1,2-units.
The Chemistry of Vulcanization. VII. Role of Zinc Butyrate in the Reaction of Diphenylmethane, Sulfur and 2-Mercaptobenzothiazole
Authors: Tsurugi Jitsuo , Fukuda Haruko
Published: February 2011

In previous Parts of this series, the accelerating mechanism of thiazole type accelerators, namely, 2-mercaptobenzothiazole (MBT), 2,2′-benzothiazolyl disulfide (MBTS) and zinc salt of 2-mercaptobenzothiazole (ZMBT) in the absence of zinc oxide or zinc soap, was investigated with diphenylmethane (DPM) as a model compound of rubber hydrocarbon. The significance of DPM as a model was discussed in some of the earlier papers. Parts IV, V and VI of this series indicated that 2-mercaptobenzothiazolyl radical generated from accelerators splits the sulfur ring, and that the processes by which accelerators generate the radical differ with each other according to their types. These results were obtained in the absence of zinc oxide or zinc soap. The present study will report the role of zinc butyrate in the reaction involving DPM, sulfur and MBT. Experience in the industry indicates that zinc oxide (or zinc soap) is indispensable to the thiazole type accelerators and that the efficiency of zinc oxide or soap is more prominent in MBT than in MBTS or ZMBT. The results obtained in the previous papers also suggest that zinc oxide or soap may have an influence on the rate at which the accelerator generates 2-mercaptobenzothiazolyl radical, since it is shown in Parts IV, V and VI that the radical has an accelerating effect. Therefore, it may be considered that zinc oxide or zinc soap activates MBT more effectively than does the other thiazole type accelerators in order to produce this radical. As will be seen later in this study, interaction of MBT with zinc butyrate in the absence of sulfur produces ZMBT and butyric acid. The ZMBT will interact with sulfur and generate the 2-mercaptobenzothiazolyl radical as reported in Part VI. The zinc salt thus formed will be dispersed in a state of molecular dispersion in the reaction system, while the same compound prepared in Part VI was not dissolved in DPM even at the reaction temperatures. In this respect the former is considered more effective than the latter. In order to verify the above assumptions the reaction involving DPM, sulfur and MBT in the presence of zinc butyrate were investigated. The reaction products and mechanism were compared with those in the absence of zinc soap. Since zinc butyrate is soluble in the reaction system at the reaction temperatures, a kinetic study also was carried out and compared with that in the absence of zinc soap.
The Vulcanization of Butyl Rubber with Phenol Formaldehyde Derivatives
Authors: Tawney P. O. , Little J. R. , Viohl P.
Published: February 2011

Butyl rubber vulcanized with 2,6-dimethylol-4-hydrocarbylphenols or condensation polymers derived therefrom shows exceptional thermal stability. This offers a means of obtaining economical and highly heat resistant vulcanizates. Vulcanizates prepared in this manner resist aging from four to ten times as well as do vulcanizates prepared with sulfur and sulfur vulcanization accelerators. It is estimated that the upper temperature limit of serviceability of butyl rubber may be increased by 100° F through the use of this vulcanization system.
Oxidation of Hevea Vulcanizates Containing Carbon Black
Authors: Bevilacqua E. M.
Published: February 2011

The oxidation of unvulcanized natural rubber and of other Jong-chain polyisoprenes proceeds through cyclic peroxidic intermediates whose detailed structure depends upon the temperature of oxidation. The principal product is a hydroperoxide. At low temperatures high yields of stable hydroperoxides may be obtained. Their structure was characterized by the work of Bolland and Hughes on squalene peroxide. The structure of the low temperature peroxide formed in rubber has not been investigated directly because of analytical difficulties. Moderate yields can be obtained; and its properties are consistent with a structure similar to that formed from squalene. At very high temperatures, the predominant cyclic intermediate has a different structure from that formed at low temperatures. It apparently is not converted to a stable hydroperoxide, but rather an intermediate radical decomposes directly, leading to breakage of carbon-to-carbon bonds in the hydrocarbon chain. This conclusion is not fully established experimentally, but consideration of the structure of the probable intermediate, suggests that a “zipper effect” should be found, leading to high yields of low molecular weight products per apparent scission, if the intermediate RO4 resulting from successive additions of two oxygen molecules has significant stability. The observed yields correspond instead to a primary yield of one molecule of scission products per scission. Associated with this decomposition is a group of low molecular weight compounds, including levulinaldehyde, formaldehyde, formic acid, acetic acid, carbon dioxide, and (by inference) water. The yield of each of the compounds depends to some extent on the experimental arrangement used to study their formation, but under a given set of conditions yields of one or more of these compounds form a good index of scission reactions in the hydrocarbon chain. So far as is known the ratio of scission to other reactions of the polymer with oxygen is determined solely by temperature, through its effect on the ratio of “low temperature” to “high temperature” peroxide intermediates.