bluuebunny/crossref_metadata_2025_split huggingface dataset:
Friction of Rubber
Authors: Gough V. E. 
Published: February 2011

Abstract
It is not intended in this paper to attempt to mention all the wide variety of aspects of rubber friction which have been discussed in the literature. The objective is to draw attention to two interesting aspects, namely, that the maximum friction does not arise until some movement occurs and that, in the general case, velocity alone is not the sole deciding factor but rather that the friction developed is a function of a ratio of velocities. These phenomena appear to be fundamental to the behavior of rolling wheels and other dynamic friction problems. In special cases, more particularly those in which the relative sliding velocities are high, the frictional phenomena reduce to being velocity dependent. Experiments show that, while consistently high friction values are obtained at slow sliding speeds on rough emery cloth and similar surfaces (coefficients of 0.9– 1.5 say), the highest coefficients (2.5– 3.0 or even more) at slow sliding speeds are obtained on smooth glass and other materials with a glass-like surface (e.g. highly polished bakelite) provided the surfaces are clean and dry and the rubber surface is free from bloom or wax. This is consistent with the view that a high coefficient of friction is obtained provided the rubber itself makes contact with the other solid in some areas at least. Provided such surface films as are present are broken through, at least in some places, the necessary intimate contact is made and a high friction obtained. To ensure intimate contact between the main mass of rubber and a body with a smooth surface, both surfaces must be clean and dry or the rubber be shaped with a tread pattern capable of exerting a wiping action to remove the surface film. Not all surface films can be removed in this manner. For example, bloom on the rubber needs to be cleaned off in other ways, such as by rubbing with a rag dipped in solvent. In the case of rough or coarse textured materials the high stresses developed on the points of the surface ensures intimate contact by breaking through the surface films, even including bloom on the rubber. The presence of surface films of any kind would be expected to reduce the friction developed because in those areas in which they carry load they provide a medium of lower tangential shear strength than the bulk of the rubber and in many cases virtually act as a lubricant carrying the normal load with very low tangential drag. The suggestions above explain the small importance of cleanliness in the case of rough surfaces and the greater importance in the case of a smooth surface. The explanations agree, at least qualitatively, with the observation that the highest frictions are obtained on clean, smooth surfaces as then the maximum actual area of contact is possible.
The Role of Free Radicals in Low Temperature Vulcanization of Butadiene Rubber
Authors: Dogadkin B. A. , Belyaeva E. N. 
Published: February 2011

Abstract
1. Elementary sulfur, liberated in the nascent state at room temperature in the reactions of MBTS with H2S, of benzoyl peroxide with H2S and SO2 with H2S, does not bring about vulcanization of butadiene rubber. In the case of the system MBTS/H2S we observe combination of sulfur in amounts 1.2 to 1.6% to a small portion of the rubber, which does not lead to structurization. The main part of the rubber (about 90% by weight) does not, according to spectroscopic analysis, alter. The combination of sulfur with rubber observed in this case takes place, apparently, according to an ionic mechanism. 2. Low-temperature vulcanization (structurization) of rubber by the system MBTS/H2S becomes apparent with prior irradiation of solutions of rubber containing disulfide with diffuse or ultraviolet light. The rate of structurization depends upon the duration of irradiation and is governed by the interaction with the H2S of the polymeric rubber radicals which are formed as a result of the dehydrogenation of the rubber by the benzothiazolyl radicals which are formed in the photodissociation of the disulfide. 3. Structurization of rubber by the system benzoyl peroxide/hydrogen sulfide is observed in the presence of an amine, in particular PBNA, necessary for the formation of free benzoate radicals as a result of the reaction of the peroxide with the amine. The peroxide in the present case acts similarly to the benzothiazolyl radicals in the case of the system MBTS/H2S. 4. Peachey type low-temperature vulcanization (SO2/H2S) proceeds in the presence of the peroxides of the rubber itself. Prior heating of the solutions of rubber upsets structurization. 5. In the vulcanization of rubber by the systems MBTS/H2S and benzoyl peroxide/hydrogen sulfide we observe combination of sulfur with the rubber in amounts of 0.6 to 0.7% and a considerable loss of double bonds, reaching 60% for 1:4 type bonds and 75% for 1:2 type bonds. 6. Radical chain interaction schemes are put forward for the processes of low-temperature structurization (vulcanization) of rubber under the action of the systems MBTS/H2S, benzoyl peroxide/hydrogen sulfide and SO2/H2S. 7. The reaction of benzoyl peroxide with PBNA is studied. A new compound, O-benzoyl-N-phenyl-N-2-naphthylhydroxylamine, is obtained, which is a powerful inhibitor of rubber oxidation.
Determination of Di-O-Tolylguanidine Dicatechol Borate in Rubber Compounds
Authors: Collins J. Oliver , Goethel Walter R. , Hei Jacob O. 
Published: February 2011

Abstract
Since knowledge of the presence of an antioxidant in a rubber stock is important in its subsequent treatment, a rapid, and at least semiquantitative method of analysis for it is desirable. At this institution two spot tests have been devised to determine the presence of the di-o-tolylguanidine salt of di-catechol borate (DOTG-DCB), known commercially as “Permalux”. One test is applicable to cured rubber stock, the other to uncured stock. No other simple method of analysis for DOTG-DCB has been available. The formula assigned to DOTG-DCB is (see PDF for diagram) The presence of DOTG-DCB in uncured stock is detected by the immediate production of a yellow color upon coupling with diazobenzenesulfanilic acid; a positive test in cured stock is the development of a blue color at low concentrations, or an aqua color if not present, when the stock, acetone treated, is treated with sodium hydroxide. If DOTG-DCB is present in very large amounts no color is produced. From the intensity of the colors developed, by use of color standards, it is possible to estimate semiquantitatively the amount in the stock.
Stress Relaxation Studies of Scission in Rubber Vulcanizates
Authors: Mercurio A. , Tobolsky A. V. 
Published: February 2011

Abstract
Deterioration of many vulcanized hydrocarbon rubbers is known to be due to reaction with molecular oxygen. Such a process is independent of oxygen concentration down to several mm of oxygen pressure and hence proceeds quite readily in an air atmosphere provided that experiments are conducted with thin enough samples to eliminate oxygen diffusion effects. Two chemically distinct loci for attack by oxygen are available. These are the crosslinked sites which are added during the vulcanization process and the network chains which are essentially the same as in the unvulcanized material. The prime objective of this study is to show clearly that vulcanized natural rubber suffers oxidative scission predominantly along the polyisoprene chains and not at the crosslinked sites as proposed by Berry and Watson. Other literature has appeared which indicates that this important point needs further clarification. Stress relaxation experiments, which measure the rate of breaking of the weakest chemical bonds recurring throughout the structure, have been utilized. If the crosslinks are oxidized, then similar rates of scission should be obtained for different chain structures so long as the common crosslink is present in all of them. On the other hand, if chains are oxidized, then rates of scission should be essentially independent of the crosslinking agent used but rather depend markedly on each chain structure. The five chain structures used in this study are depicted in Table I. In each case at least a few per cent of double bond-containing segments are present in the main chain to allow for ordinary chemical vulcanization methods. All of these have been crosslinked by sulfur and by a nonsulfur containing agent.
Mastication. IX. Shear-Dependence of Degradation on Hot Mastication
Authors: Mullins L. , Watson W. F. 
Published: February 2011

Abstract
The rate of degradation of rubber during mastication is minimal at about 115° C, degradation increasing progressively on lowering or raising the temperature as far below or above this temperature as practicable. Designation of the degradation processes with the negative and positive temperature coefficients as “cold” and “hot mastication”, respectively, is supported by differences in their chemical mechanisms. The essential degradation step of cold mastication is rupture of rubber molecules by the imposed deforming forces to radicals which are converted to the degraded molecules after reaction with oxygen or other radical acceptor present in the rubber. Hot mastication is less well understood; scission appears to be by an oxidative reaction, with the implication that mastication serves in the main to expose fresh surfaces for absorption of oxygen. The mechanicodegradation of cold mastication produces an unusually rapid decrease in viscosity with molecular weight, logarithmic plotting of these two quantities giving an apparent α, according to the relation [η]=KMα, of greater than unity. The value of α for fractionated rubber is 0.67. The apparent high α is most readily explicable by a decrease in K on degradation, while α has its normal value of 0.67 for natural rubber. A decrease in K would occur if the molecular weight distribution around the mean became sharper. This distribution change has been considered to be caused by rupture only of molecules above a certain molecular weight, and this in the central sections of the molecules. For the oxidation of thin films and latex or any other chemical process whereby scission conceivably occurs with equal probability at every monomeric unit, the chain-length distribution would tend to a random one. In particular, if the rubber had initially a random distribution, viscosity-molecular weight decrease would yield an α equal to that for fractionated rubber and a K which is Γ (α + 2) times higher. Viscosity-molecular weight data on hot mastication have not been previously published. If a normal chemical degradation takes place, a difference in the viscosity-molecular weight relationship from that on cold mastication should be detectable. Differences in molecular weight distribution should also be reflected in differences in other properties of masticated rubber and, to a lesser extent, of vulcanized products. A comparison of viscosity-molecular weight relationships and other properties of rubbers masticated in air forms a starting point for answering the complex query of the relative merits of cold and hot mastication. Interaction of rubber with fillers and vulcanizing ingredients would then have to be systematically investigated.
Measurement of the Dynamic Modulus of Rubber at Very Small Amplitudes with an Optical Interferometer
Authors: Borovitskaya N. M. 
Published: February 2011

Abstract
A method of measuring very small differences of optical path using light modulation by an interferometer has been described. This enables one to measure amplitudes of mechanical vibrations of the order of 0.01 A or even smaller. We have used this method to measure the dynamic modulus of rubber at very small amplitudes. It is desirable to use this method for measuring the dynamic modulus of rubber and other highly elastic substances, firstly because in accuracy and simplicity it has certain advantages over existing acoustic methods. In the second place, it enables one to work at very small amplitudes and, in association with other methods, over a very wide range of amplitudes of deformation. This is of interest in connection with the general theory of the dynamic properties of rubber, and in particular, for checking the linearity of these properties, that is, the independence of the modulus and the loss on the amplitude, in particular for filled rubbers. We will briefly describe the apparatus with which the measurements were made. It consists of a Michelson interferometer and a source of monochromatic light. The interference pattern (lines of equal width) is projected onto the cathode of a photomultiplier. The output of the photo multiplier is fed to the input of a narrow-band filter, to the output of which the measuring instrument is connected. The mirror on the interferometer is set up so that the whole of the interference pattern, or the greater part of it, is uniformly illuminated. If now one of the mirrors vibrates with a frequency ω and an amplitude of z, then the difference in path between the interference beams will vary with a frequency of ω and the intensity of the light falling on the photomultiplier will also change. The current through the photomultiplier will be modulated with a frequency of ω. The first harmonic of the photocurrent will be I1=AJ1(4τz/λ), where λ is the wavelength of light; A is a coefficient depending on the intensity of the interfering beams and on their difference of path with the mirror at rest; I1 is a first order Bessel function.
Stress Waves and Fracture Surfaces
Authors: Andrews E. H. 
Published: February 2011

Abstract
Surface markings observed in the brittle fracture of certain frozen rubbers display striking, wavelike characteristics. They have been identified as “Wallner” lines, caused by the interaction of the fracture front with stress waves emanating from the region of the fracture front itself. These oscillations are possibly caused by the supply of excess energy to the fracture tip. A value of approximately 1:2 is obtained for the ratio of fracture velocity to wave velocity.
Vulcanization of Elastomers. 24. The Effect of Fillers on the Course of Vulcanization Reactions. I
Authors: Scheele Walter , Mau Günter , Kemme Gregor 
Published: February 2011

Abstract
The effect of Aerosil on the chemical reactions and the kinetics observed in thiuram vulcanizations was subjected to closer scrutiny. Results now available show: 1. Aerosil does not alter the chemical mechanism of thiuram vulcanizations. It also has no qualitative effect on the kinetics of the various reactions involved. Thiuram disappearance and dithiocarbamate formation over by far the greatest range of conversions are first order reactions. Nevertheless, the limiting value of dithiocarbamate formation is somewhat higher than in the absence of Aerosil. 2. Quantitatively speaking, essential differences are involved. The rate constants for both thiuram loss and dithiocarbamate formation rise considerably when Aerosil is used; in both cases there is a dependence on the Aerosil content of the rubber compound. Yet the activation energies of thiuram disappearance and dithiocarbamate formation are practically the same as in Aerosil-free thiuram vulcanizations, amounting to about 21 kcal/mole. 3. Measurements of the limiting equilibrium swelling reveal that adding Aerosil does not result in additional crosslinking, so that in thiuram vulcanizations the catalytic action displayed by silica gel is the outstanding feature.
Vulcanization of Rubber in the Presence of N,N-Diethyl-2-Benzothiazolylsulfenamide as Accelerator
Authors: Dogadkin B. A. , Beliatskaya O. N. , Dobromyslova A. B. , Feldshtein M. S. 
Published: February 2011

Abstract
1. The vulcanization of rubber in the presence of N,N-diethyl-2-benzothiazolylsulfenamide is characterized by an S-shaped curve for the addition of sulfur with an initial induction period in the reaction. The modulus and number of crosslinks are changed in an analogous manner to the structure of the vulcanizate. 2. The energy of activation of the addition of sulfur in the initial period is equal to 30 kcal per mole as against 14 kcal per mole in the main period. 3. The induction period is increased if the sodium-butadiene rubber is purified from alkali. 4. Molecular oxygen present in the compound being vulcanized decreases the induction period and increases the rate of the addition of the sulfur in the main period. An induction period is not observed when vulcanization is carried out in an atmosphere of pure oxygen. 5. The interaction of N,N-diethyl-2-benzothiazolylsulfenamide with rubber (in the absence of sulfur) at vulcanization temperatures is accompanied by the formation of MBT, diethylamine, and the addition of the elements of the accelerator to the rubber. The kinetics of this process were studied. 6. The interaction of N,N-diethyl-2-benzothiazolyl sulfenamide with rubber leads to the formation of chemical crosslinks between the molecules of rubber (the effect of vulcanization). 7. The change of N,N-diethyl-2-benzothiazolyl sulfenamide under the conditions of normal sulfur vulcanization has the same character as in the interaction of it with rubber. The kinetics of the formation of MBT have a maximum which coincides with the maximum rate of the addition of sulfur to the rubber. 8. A mechanism is presented for the vulcanization and acceleration actions of N,N-diethyl-2-benzothiazolyl sulfenamide which provides for the extraction of hydrogen by the accelerator radicals from the molecular chains of the rubber with the formation of MBT, diethylamine and polymer radicals which are able to interact with the sulfur.
The Action of Binary Accelerator Systems of Vulcanization
Authors: Dogadkin B. A. , Feldshtein M. S. , Belyaeva E. N. 
Published: February 2011

Abstract
1. It was established that in the joint use of vulcanization accelerators there takes place mutual activation of the accelerators, activation of one accelerator or additive action depending on the chemical structure of the accelerators. 2. Of the studied combinations of vulcanization accelerators the systems showing mutual activation are disulfides or mercaptans with nitrogen containing organic bases, and disulfides with sulfenamides. Sulfenamides with nitrogen containing organic bases result in activation of one of the accelerators. Examples of systems of accelerators with additive action are combinations of sulfenamides or disulfides with TMTM. 3. It was established that in the case of systems with mutual activation, such as MBTS with DPG or with CHBTS, the reaction between the accelerators produces MBT. For such systems, greater yields of MBT were observed under vulcanization conditions than were obtained by action of the accelerators alone. This indicates that the principal result of the chemical reaction of the accelerators is the formation of free radicals which are capable of splitting hydrogen from the rubber molecule with the formation of rubber high polymer radicals. 4. There is presented a tentative scheme for a radical mechanism of the joint action of vulcanization accelerators for the case where mutual activation of accelerators exists.
Composition of Vulcanizing System, Course of Vulcanization and Bond Strength of Plied-Up SBR
Authors: Dogadkin B. A. , Feldshtein M. S. , Pevzner D. M. 
Published: February 2011

Abstract
Insufficient bond strength between individual plies, in particular between the breaker strip and tire tread, is one of the shortcomings of tires manufactured from SBR rubbers. For several reasons, one of which is the conditions in which such large articles as tires are vulcanized, the breaker strip contains a much more active vulcanizing system than the tread rubber. The vulcanization of these rubbers in a zone of direct contact is effected at virtually the same temperature. In considering the special features of the vulcanization of SBR rubber, as one which vulcanizes comparatively slowly, it was natural to expect that the different activities of the vulcanizing systems in joined plies condition a sharp difference in the course of vulcanization, which might affect the bond strength considerably. We therefore made a study of the effect of the composition of crosslinking system and kinetics of vulcanization on the bond strength of plied-up SKS 30 rubber.
The Crosslinks in TMTD-Zinc Oxide-Natural Rubber Vulcanizates
Authors: Moore C. G. 
Published: February 2011

Abstract
The mechanism of vulcanization of natural rubber (NR) by means of tetramethylthiuram disulfide (TMTD) and zinc oxide has been the subject of much recent experimental work and speculation. While such studies have clarified the kinetics and stoichiometry of TMTD decomposition and zinc dimethyldithiocarbamate formation, they have not directly aided our knowledge of the nature of the crosslinks in the resultant vulcanizate. It was earlier suggested that the vulcanizate contained only C—C crosslinks, comparable with those formed by means of di-tert-alkyl (and aralkyl) peroxides, while more recently, disulfide crosslinks have been proposed. However, neither of these views has been confirmed by direct chemical studies of the vulcanizate. Evidence is now presented which shows that there can be no appreciable amount of C—C crosslinking by the TMTD-ZnO combination, and this is consistent with the view that sulfur crosslinks predominate. This conclusion is based on the respective swelling properties in n-decane of dicumyl peroxide vulcanizates (containing only C—C crosslinks) and TMTD-ZnO vulcanizates, which have been treated with methyl iodide in vacuo at 80° C. This reagent is known to cause the fission of C—S and S—S bonds in variously constituted organic mono- and polysulfides and should therefore cause the fission of sulfur crosslinks in a vulcanizate with consequent degradation of the network (cf. Ref. 8), whereas there is no evidence that di-allylic C—C crosslinks can be similarly degraded.
The Reaction of Tetramethylthiuram Disulfide and Monosulfide with Rubber
Authors: Dogadkin B. A. , Shershnev V. A. 
Published: February 2011

Abstract
The kinetics of the reaction of tetramethylthiuram monosulfide (TMTM) differ from that with the disulfide (TMTD). No formation of chemical crosslinks takes place; the sulfur of TMTD adds in correspondence with a curve exhibiting no maximum and the addition differs in the presence and absence of zinc oxide. Simultaneously, the thermal decomposition of TMTM takes place. The electron paramagnetic resonance spectra and the reaction with geraniol show TMTD and TMTM to interact with rubber through a free radical stage.
Metal Oxides in Tetramethylthiuram Disulfide Vulcanization
Authors: Dogadkin B. A. , Shershnev V. A. 
Published: February 2011

Abstract
Rubber is usually vulcanized with the aid of the so-called activators, metal oxides, zinc oxide being the one most often used. In vulcanization in the presence of MBT (mercaptobenzothiazole) or DPG (diphenylguanidine) as accelerators it was found that vulcanization activators have almost no effect on the rate of addition of sulfur to rubber, but have a significant influence on the rate and degree of crosslinking of the rubber molecules. Special interest attaches to studies of the action of metal oxides in vulcanization with tetramethylthiuram disulfide (TMTD), as it is known from actual practice that in the absence of zinc oxide this accelerator does not bring about vulcanization. Vulcanization with TMTD was studied on mixtures of natural rubber (extracted with cold acetone in a stream of nitrogen for 50 hours) and of synthetic isoprene rubber (SKI) masticated on microrolls, of the following compositions (in parts by weight).