bluuebunny/crossref_metadata_2025 huggingface dataset:
A Rugged Semiautomatic Extensometer for Rubber
Authors: Donnelly P. I.
Published: February 2011

The evaluation of an elastomer—new or established—inevitably involves a study of tensile properties. ASTM procedure D 412 is generally used as a guide for the tensile testing of vulcanized rubber. In this method, an operator observes bench marks on the sample and records the modulus at every 100% elongation, the ultimate elongation, and the tensile strength at break. An extensometer has been developed to eliminate operator coordination and judgment factors from rubber tensile testing. It is simple and sufficiently rugged for routine testing. Its features are a counterbalanced guide rod with a sliding electrical contactor, and specimen followers which automatically unlatch to avoid being damaged when specimens break. In addition there is a counter for direct digital indication of elongation, and an electrical circuit which controls a short duration spark to mark the autographic chart. Experience in testing up to 5000 specimens per year has shown that the apparatus makes an inexperienced operator as effective as trained operators working under optimum conditions. The instrument has been used successfully on materials ranging from soft rubber to plasticized and filled poly (vinyl chloride).
Thermal Conductivity of High Polymers from −180° C to 90° C
Authors: Eiermann K. , Hellwege K.-H.
Published: February 2011

The thermal conductivity of plastics is relatively small and for this reason not easily measured. That is why the results in the literature vary sharply. Therefore measurements were made in the German Plastics Institute of the thermal conductivity of plastics with different methods and the results checked against each other. As the overall agreement is very good, we shall give the results only from a quasistationary method which works over a large temperature range. A good thermal contact at the surface of the sample is decisive. Therefore we had to abandon high vacuum as thermal insulation in favor of helium gas, which gives a good and exactly evaluated thermal contact. Thermal losses to the outside had to be prevented by guard rings. We deal first with amorphous high polymers. Their thermal conductivity varies only slightly with temperature even if one goes through the second-order transition region. However, a break in the curve of the thermal conductivity, is characteristic that is to say, a jump of the thermal coefficient at the second-order transition temperature. Figures 1–3 show this for natural rubber, Vulkollan (a crosslinked polyester-urethane elastomer), polyisobutylene, and polyvinyl chloride with different contents of plasticizer. The dependence on the concentration of plasticizer is the same for the break in the thermal-conductivity curve as for the second-order transition temperature. The systematic variation of the thermal conductivity with temperature which has been described seems to be valid in general for amorphous substances with molecules which have the form of a chain. For instance, even selenium, when displaced from the melt, Figure 4, passes smoothly through the second-order transition point without the extreme maxima and minima which have been seen by other authors and which are due to peculiarities in the experimental arrangement used.
High Resolution Nuclear Magnetic Resonance Spectra of Various Polyisoprenes
Authors: Golub M. A. , Fuqua S. A. , Bhacca N. S.
Published: February 2011

There has been some controversy recently as to whether hevea and balata (or gutta-percha) macromolecules comprise 100 per cent 1,4 units, or whether they are predominantly cis and trans structures, respectively, with minor amounts of isopropenyl or 3,4 units. Binder contends, on the basis of a small absorption peak at 11.25 µ in the infrared spectrum of each of these polymers, that the hevea and balata macromolecules contain 2.2 and 1.3 per cent 3,4 units, respectively. This has been disputed by Fraga who showed that there was no evidence for isopropenyl groups in the near infrared spectra; he therefore concluded that the natural polyisoprenes are essentially pure 1, 4-type polymers. Another interesting Question which has never been resolved is whether the 1,4 units in hevea (or balata) are exclusively cis (or trans) or whether these polymers contain a small amount of the opposite isomer as an impurity. Recent developments in high resolution n.m.r. work on polymers, and in particular, the application of n.m.r. to an analysis of butadiene—isoprene copolymer compositions, have prompted us to examine these questions with the aid of this tool. The present communication reports the results of an investigation of hevea and balata microstructure using a Varian high resolution 100 Mc. n.m.r. spectrometer as well as a Mnemotron Computer of Average Transients (C.A.T.) attached to a Varian A-60 spectrometer.
Flexibility and Shape of Macromolecules
Authors: Tsvetkov V. N.
Published: February 2011

The main feature of high molecular weight substances is the great size, chain structure and flexibility of the molecules. Investigation of macromolecules flexibility must be regarded as one of the most important tasks in the investigation of the structure of polymers. In the present article we shall deal quite briefly with certain results achieved in this field, which seem to us to be of fundamental importance. The cause of the flexibility of polymeric chains is the existence of a certain freedom of rotation around the valency bonds of the atoms making up the molecule. Nevertheless, this rotation is always more or less hindered by forces which may be either intramolecular (between the atoms of one and the same chain), or else inter-molecular (between atoms of a given chain and their molecules of the surrounding medium). It is possible to a certain extent to separate the influence of these forces from each other, by studying and comparing the properties of macromolecules in solutions (using different solvents) and in the solid phase. Here, nevertheless, we must keep in mind the difference between thermodynamic (equilibrium) and kinetic (nonequilibrium) flexibility of the polymer chain. The deduction of equilibrium flexibility is made on the basis of investigation of configurations (the dimensions and geometrical shape) of macromolecules in solution in the statistically equilibrium state; and of the kinetic, on the basis of investagation of the rate of the processes which convert the macromolecules from one equilibrium configuration to another. The vast majority of experimental work dealing with the determination of kinetic flexibility has been carried out for polymers in bulk (mechanical and dielectric relaxation processes). In this case the influence of the intermolecular reactions is just as great as that of the intramolecular forces, and therefore it is very difficult to separate these two effects. Therefore at the present time we have at our disposal for the determination of equilibrium flexibility of polymer chains considerably more experimental and theoretical possibilities than is the case for kinetic flexibility.
Static Friction and the Law of Rubber Friction
Authors: Lavrentev V. V.
Published: February 2011

a) The true static friction of vulcanized rubber is in practice immeasurably small (equal to zero, according to theory). b) The static friction as usually determined is an initial friction force. c) The initial friction force is equal to the sliding friction force in accelerated movement. It depends on the contact time, the rate of growth of the tangential force and the other conditions of experiment. d) With long contact times, particularly at higher temperatures, strong chemical bonds are formed between the vulcanized rubber and the track, leading to true static friction. e) The theoretical law of friction agrees well with the experimental results over the whole range of normal pressures. f) Good approximations are given in the range of low normal pressures by Coulomb's law (5) and in the rubber of high normal pressures by that of Thirion (7).
Relaxation Processes in Vulcanized Rubber. I. Relations between Stress Relaxation, Creep, Recovery, and Hysteresis
Authors: Gent A. N.
Published: February 2011

An experimental study is described of stress relaxation, creep, recovery, and hysteresis in vulcanized rubbers under moderate deformations. The measurements indicate that the rate of stress relaxation is substantially independent of the amount or type of deformation for moderate deformations, and is simply related to the hysteresis. The rates of creep and recovery are found to be in good agreement with values calculated from the form of the load—deformation relationship and the (constant) value of the relaxation rate.
Relaxation Processes in Vulcanized Rubber. II. Secondary Relaxation Due to Network Breakdown
Authors: Gent A. N.
Published: February 2011

An experimental study is described of a “secondary” relaxation process in stretched vulcanizates, which becomes dominant after long periods at normal temperatures. It is shown to be affected markedly by the temperature, the atmosphere in which the test is conducted, and the presence of oxidation inhibitors. It is therefore attributed to oxidative deterioration of the molecular structure. In some vulcanizates, however, a similar or even greater relaxation is found to occur in vacuo, and this is attributed to the failure of specific crosslink structures. The extent of recovery on releasing the extended testpieces has also been investigated for a number of natural rubber vulcanizates.
Some Chemical Effects in Fatigue Cracking of Vulcanized Rubbers
Authors: Gent A. N.
Published: February 2011

An apparatus is described for studying the fatigue of rubber strips under repeated simple extensions in different atmospheres. The fatigue life is shown to be greatly increased in vacuo for vulcanizates of natural rubber and SBR. The effect of oxidation inhibitors and radical acceptors has been examined; they are found to prolong the life in air, but have little effect in vacuo. The results suggest that a substantial proportion of crack growth in air is due to oxidative deterioration of the rubber at the crack tip, probably initiated by mechanical rupture.
Dynamic Strain Effects in Elastomers
Authors: Warnaka Glenn E.
Published: February 2011

Many common elastomeric materials have two ranges of dynamic-mechanical behavior. Such materials behave as viscoelastomers at very small strains and as plastoelastomers at strains of practical engineering interest. The change from viscoelastic to plastoelastic behavior occurs at dynamic strain amplitudes of 0.001 inches per inch to 0.005 inches per inch. In the plastoelastic range, the dynamic elastic modulus decreases with increasing dynamic strain amplitude. Loss factor reaches a maximum in the plastoelastic range.
Sinusoidal-Strain Dynamic Testing of Rubber Products
Authors: Payne A. R.
Published: February 2011

This paper is concerned with methods for evaluating the dynamic modulus and hysteresis of rubber under a wide range of conditions. The original machine in use at the Rubber and Plastics Research Assn. (RAPRA), and then its commercially available counterpart, the Wallace electronic sinusoidal-strain dynamic tester, are described. Some typical results obtained with the first machine, but obtainable with either, are given.
The Dynamic Properties of Carbon Black-Loaded Natural Rubber Vulcanizates. Part I
Authors: Payne A. R.
Published: February 2011

The dynamic properties of a natural vulcanized rubber containing carbon black were studied for dynamic tensions of amplitude varying greatly. It was shown that both the elastic responses and viscosity change with amplitude of oscillation and with concentration and type of carbon black. The effects of thermal treatment on the dynamic modulus were also studied. Beginning with conditions of equilibrium between the hard and soft regions of the vulcanizate for very weak stresses, the values for the formation of hard regions from soft regions were determined by means of the Van't Hoff isochore.
The Dynamic Properties of Carbon Black Loaded Natural Rubber Vulcanizates. Part II
Authors: Payne A. R.
Published: February 2011

The dynamic shear modulus at very high strains, (G∞), of carbon black filler loaded vulcanizates is regarded as due to the product of two factors : (a) a hydrodynamic interaction due to filler particles, and (b) a second factor for which evidence is given suggesting that it arises from a few strong linkages which are known to link filler particles to the matrix. Experimentally a measure of (a) has been obtained from model vulcanizates using glass spheres as the filler, and of (b) from equilibrium swelling measurements on rubber vulcanizates containing carbon black. Quantitatively, the difference between the shear modulus of the pure gum vulcanizate, Gpure gum, and G∞ can be explained by these measurements.
An Elution Chromatography Technique for cis-1,4-Polybutadiene
Authors: Hulme J. M. , McLeod L. A.
Published: February 2011

Experiments are described to show that cis-1,4-polybutadiene can be fractionated using the elution chromatography technique of Baker and Williams. Changes have been made to the equipment to give easier and more reliable operation. A method of selecting solvents and precipitants is described and it is shown that by proper selection of solvent and precipitant, the resolution of the higher molecular weight fractions may be improved. The influence on the fractionation of temperature, concentration of polymer in the eluant and column loading are investigated. It is concluded that column loading is the most important factor in explaining reversals of limiting viscosity number in the fractionation results.
Atmospheric Ozone in Helsinki and Its Effects on Rubber
Authors: Soininen Antti , Pehu-Lehtonon Anna-liisa , Auterinen Elli
Published: February 2011

Although the amount of ozone in the atmosphere is rather small compared with other gases its importance in several respects is rather great. This is mainly due to the high absorption and reacting capacities of ozone. The absorption capacity becomes apparent among other ways in the fact that the ozone layer of the atmosphere absorbs the excessive ultraviolet radiation coming from space as well as heat radiation from the earth. On the other hand, the reacting capacity can best be observed in numerous harmful oxidation phenomena, among which a typical example is the cracking of the surface of rubber products, caused by ozone. Generation and distribution of ozone in the atmosphere.—It is assumed that ozone is generated in the upper atmosphere photochemically under the influence of ultraviolet radiation. The shortwave ultraviolet radiation of a wavelength of about 2000 A breaks the oxygen molecules into atoms that combine with other oxygen molecules to form ozone. The ozone in turn absorbs ultraviolet radiation of a longer wavelength, which again breaks up the ozone thus maintaining an equilibrium in the concentration. This equilibrium is largely dependent upon temperature, the lower temperatures giving rise to a considerably higher concentration of ozone than the higher temperatures. The maximum concentration of ozone in the atmosphere is at an altitude of about 20 kilometers from the earth. The distance of this maximum from the surface of the earth, however, varies over different parts of the globe and according to the season. There is a constant movement of ozone from the actual ozone layer to the lower air regions near the surface of the earth. The major part of the ozone is destroyed near the earth's surface, as it comes into contact with oxidizable matter. Generally speaking, this movement of the ozone into the lower parts of the atmosphere is caused by turbulence, that is, by mixing of the air masses. In the atmosphere there is a regular circulation between the different regions. Near the equator the direction of the movement is upwards, from the troposphere to the stratosphere, while around the latitude 60 it is the other way around. This phenomenon explains, for example, the relatively large increase in radioactivity in polar districts and, in addition, it offers a partial explanation of the high ozone concentration near the surface of the earth in these parts compared with that in warmer regions.
Ozonation of Atactic Polypropylene
Authors: Lazar M. , Pavlinec I. , Manasek Z. , Micko M. , Berek D.
Published: February 2011

1. It is determined by study of the accumulation of peroxides in atactic polypropylene that ozone acts as an initiator of oxidation and considerably accelerates the course of the reaction even at room temperature. 2. The surface of the oxidized specimens is an important kinetic factor in the accumulation of the peroxides. 3. In addition to the formation of hydroperoxides in the initial phases of the process there takes place a crosslinking of the surface layer of the oxidized films by polymeric peroxides. These peroxides gradually decompose with the simultaneous formation of hydroperoxides. 4. The degradation of macromolecules under the action of ozone is less than in oxidation by the atmosphere.
The Compounding of Styrene—Butadiene Rubber with Shellac
Authors: Saxena K. K. , Banerjee S.
Published: February 2011

It has been possible to incorporate shellac up to 25 phr in OE-SBR without any difficulty on a roll mill by properly adjusting the temperature of rolls. Shellac acts as a lubricant and a processing aid at higher temperatures. A higher amount of shellac can be used safely as the stock becomes less and less scorchy. It improves tear resistance, tensile strength and hardness of the gum stock. Greater abrasion loss may restrict its use even though other properties are rather good. Due to the presence of lac dye in shellac stocks of different pastel shades may be obtained. From the present study it appears that shellac may be used as an extender and may replace rubber by 20 parts quite advantageously.
Vulcanization of Carboxylic Rubbers
Authors: Zakharov N. D.
Published: February 2011

1. A study of a series of substances contributing to structure formation was carried out. The most active of these materials were shown to be aluminum chloride, caustic soda, caustic potash, calcium oxide, magnesium oxide and calcium hydroxide. 2. It was shown that the quantity of chemical crosslinks in metal oxide vulcanizates of carboxylic rubbers was significantly less than in corresponding sulfur vulcanizates. 3. The number of crosslinks in the steric network of the vulcanizates depend on the form of the vulcanizing agent. Magnesium oxide gave the densest three dimensional structure. 4. It was shown that nonchemical intermolecular bonds play a significant role in the formation of structures of carboxylic rubbers. The assumption that these bonds could be of the hydrogen, van der Waals and coordination types was expressed.
Agglomeration and Reinforcement of Synthetic Latexes by Freezing
Authors: Talalay L.
Published: February 2011

For most applications rubber latexes must have high solids content. To achieve this, with reasonable fluidity, the latex particles must be large. Limitations in the kinetics of emulsion polymerization make it desirable to polymerize a small particle latex and postagglomerate to a larger size. This paper deals with the process of freezing and thawing a latex under controlled conditions which result in a substantial increase in particle size. The variables controlling the process such as soap coverage of the particles, pH, freeze duration, and freeze temperature are analyzed. The type of soap used is shown to affect the lower limit of usable freezing temperature. The polymer composition and hardness are shown to affect coagulum formation and the shape of the particles after freeze-agglomeration. Coagglomeration of a mixture of rubber and resin latexes by freezing is found to result in a reinforced polymer system analogous to that obtained by carbon black reinforcement of dry rubber. The effects of the particle size and the softening temperature of the reinforcing resin are demonstrated. An optical microscopic method for observing the freeze-agglomeration process is described and an attempt is made to elucidate the mechanism of the process.
Dilatometric Determination of Polymer Compatibility
Authors: Bartenev G. M. , Kongarov G. S.
Published: February 2011

1. The temperature contraction curves for rubbery polymer mixtures define the degree of compatibility of these polymers only when the glass temperatures are not close to the same. 2. Mixtures of obviously incompatible polymers display several glass temperatures (according to the number of polymers in the mixture). The values of these temperatures coincide with the glass temperatures of the pure polymers and do not depend on the ratio of the polymers in the mixture. 3. Mixtures of compatible polymers have a single glass temperature which changes linearly with the volume ratio of the polymers. 4. The coefficient of linear expansion (contraction) of all polymer mixtures follows the additivity law within the visible limits of experimental error from sample to sample.
Relaxation Processes in Vulcanized Rubber. III. Relaxation at Large Strains and the Effect of Fillers
Authors: Gent A. N.
Published: February 2011

Some experimental measurements are described of stress relaxation and creep at room temperatures in vulcanizates of natural rubber, butyl, and SBR. In an unfilled natural rubber vulcanizate the rate of stress relaxation is found to rise sharply for extensions of more than about 200%. Reasons are given for attributing this to the growth of a crystalline phase. Similar rates are observed at all extensions for a carbon black filled natural rubber vulcanizate. This is shown to be in satisfactory accord with the Mullins-Tobin model structure for filled vulcanizates, when the whole of the observed relaxation occurs in “softened” regions at rates appropriate to the high local deformations. The failure of rubber-carbon black associations with time does not appear to constitute a major relaxation process. In noncrystallizing unfilled vulcanizates the rate of relaxation is found to decrease somewhat with extension, possibly due to finite-extensibility effects. Preliminary measurements on a filled SBR vulcanizate suggest that a significant contribution to the observed relaxation arises from progressive failure of rubber-filler associations in this case. The relation derived previously between the rates of creep and stress relaxation at equivalent deformations is confirmed in all cases, within experimental error. Its validity in highly-irreversible systems is thus established experimentally.
Elastomeric Fibers Based on Polyurethanes
Authors: Rinke H.
Published: February 2011

Highly elastic polyurethanes suitable for fiber production can be obtained by various synthetic routes based on diisocyanate polyaddition processes. Macro-diisocyanates obtained from long chain diols and diisocyanates are allowed to react with polyamides during fiber formation (chemical spinning process) or the macrodiisocyanates are treated in solvents (e.g., dimethylformamide) with polyamines to give highly viscous, spinnable solutions of polymer. Both methods yield highly elastic polymers with wide-mesh network structures. The production of polyurethane fibers and their structures and physical properties are described.
Stresses at a Crack in an Elastomer
Authors: Andrews E. H.
Published: February 2011

A microscopical, photoelastic technique has been used to investigate the distributions of stress and strain around a crack in a highly elastic material, natural rubber. The finite strains encountered in such a material give rise to a distortion of the principal-stress map, an effect which has no parallel in classical elasticity and which leads to a complex dependence of the stresses upon the external constraint. The strain energy at a point is, however, simply related to the external constraint when the latter is expressed in terms of a stored energy parameter T, which is defined. The same parameter is shown to govern the distortion of the stress field. The decay of strain energy in a direction perpendicular to the crack axis is much more gradual when the strains are finite, but the rate of decay along the axis in the elastomer is similar, both in form and magnitude, to that predicted by infinitesimal-strain theory.
Preparation of Ultrathin Sections of Polymeric Materials
Authors: Razikov K. Kh. , Markova G. S.
Published: February 2011

Much importance attaches at the present time to the use of ultrathin sections for the investigation of the structure of polymeric materials by electron microscopy, electron diffraction and other methods. Extremely thin sections (down to hundredths of a micron) can be prepared by means of ultramicrotomes in which thermal regulation of the feed of the specimen is provided. The use of ultramicrotomes in various branches of sciences has given valuable information on the fine structure of many substances. In the present article we describe the use of the ultrathin section method for the investigation of the structure of polymers by means of an ultramicrotome of the “Sjostrand Ultra-microtome LKB-Producter” type. As a result of the elasticity of polymeric materials the preparation of thin sections is rendered difficult. Therefore the development of a method of producing ultrathin sections of polymeric materials is of considerable interest. We have developed such a method for the study of the structure of thin polymeric fibers (of diameter 15 to 20 µ) of thick monofilament (of diameter 0.5 mm and above) and also of films. The technique of preparation of ultrathin sections consists of the following stages: 1) embedding the specimens for investigation; 2) preparation of the specimen for cutting; 3) preparation of the knives; and 4) preparation of the apparatus and cutting.
Kinetics of Thiazole-Accelerated Sulfur Vulcanization of Natural Rubber
Authors: Russell R. , Smith D. A. , Welding G. N.
Published: February 2011

Thiazole-accelerated sulfur vulcanization of natural rubber gum stocks has been investigated at temperatures from 110° to 140° C for times over the range 1 to 104 min. Swelling measurements on the vulcanizates were used to estimate the contribution of chemical reactions to the network chain density, (ρMc−1)chem which was plotted against cure time. The kinetic graphs show clearly an induction period (t0), then fast crosslinking, a slow limited degradation, and finally a “long-time” crosslinking reaction. Apart from the induction period, each of the kinetic graphs is satisfactorily represented by a rate equation assuming three independent additive reactions: first order crosslinking, first order partial degradation, and a long-time reaction assumed to be zero order. The method has been used to compare MBT and MBTS at equal concentration. One consistent difference is the increase of induction period with MBTS in place of MBT, accompanied by a somewhat greater increase of time of cure to maximum network density. Also the completed contributions (Xand Δ) from the initial crosslinking reaction and the degradation reaction, respectively, are greater with MBTS than with MBT. Over the temperature range studied there is no difference between MBT and MBTS in the activation energies for crosslinking, or for t0−1 or for the long-time reaction, but MBTS has a higher activation energy for degradation than MBT. With rising temperature of cure, Δ increases towards X with each accelerator.
Fluid Bed Vulcanization
Authors: Hughes B. G. , Izod D. A. W. , Moakes R. C. W. , Soden A. L. , Watson W. F.
Published: February 2011

This paper describes the use of fluidized solid particles as heating medium for rubber vulcanization, with emphasis on the continuous vulcanization of unsupported extrusions. The relevant features of fluid beds for this purpose—density, pressure and flow of gas, particle size, viscosity, heat transfer, chemical inertness—are considered. The construction and experience in the use of a horizontal trough and vertical column fluid bed are outlined. Attendant problems, notably porosity of the vulcanizate, are dealt with.
Intrinsic Viscosity-Molecular Weight Relationship for cis-1,4-Polyisoprene
Authors: Beattie W. H. , Booth C.
Published: February 2011

The intrinsic viscosity-molecular weight relationship has been determined for synthetic cis-1,4-polyisoprene prepared with butyllithium initiator. The best representation of our results is the equation,[η]=2.00×10−4(Mv)0.728 for intrinsic viscosities determined in toluene at 30° C. This relationship agrees, within experimental error, with that obtained for natural rubber by Carter, Scott, and Magat.
Influence of Chemical Modification on the Oxidizability of Natural Rubber
Authors: de Merlier Jacqueline , Le Bras Jean
Published: February 2011

The rubber hydrocarbon, which presents two reactive sites for each isoprenic unit: the double bond and the α-methylenic carbon, is highly sensitive to the action of oxygen. It is known that different products can react with rubber, some by addition on the double bonds, others by combination to the α-methylenic carbons and we have attempted to determine the influence that these modifications might have on oxidizability. The reagents chosen were maleic anhydride to block the α-methylenic carbons and saligenol to saturate the double bonds. Modified rubbers containing varying proportions of these reagents were prepared and their oxidizabilities at 80° C were measured, using the manometric method. In both cases an important decrease of oxidizability was noted, which went far beyond what might have been expected from the small proportion of reactive groups combined; differences in the oxidation kinetics were also observed, according to the mode of combination to the rubber hydrocarbon of the two types of reagent used. These results show that it is possible, in this way, to improve the resistance of raw rubber to oxidation and that this will probably influence the behavior of vulcanizates.
Reaction Products of Chloral with cis-1,4-Polyisoprene
Authors: Pinazzi Christian , Pautrat Rene , Cheritat Roland
Published: February 2011

In an earlier note the fixation of chloral onto cis-1,4-polyisoprene (natural or synthetic) in the presence of a catalyst such as AlCl3 or BF3 was discussed. A similar combination with glyoxal has already been mentioned. The fixation of chloral produces macromolecular products with a level of fixation of not higher than n=30 (n, number of reagent molecules attached to a chain of 100 C5H8 units). These compounds contain hydroxyl groups, the infrared bands of which appear at 3,300–3,500 cm−1, while the chlorines are identified at 570, 620, 680, 730, and 1,080 cm−1; these bands can be attributed to side chains —CHOH—CCl3. Also, the band which is characteristic for the cis configuration remains in the spectrum, but has decreased in comparison with the blank; the broadening of the peak at 1,640 cm−1 and the presence of a band at 860 cm−1 indicate the appearance of vinylidene double bonds not located in the chain. This observation is in agreement with our earlier work. The presence of side chains —CHOH—CCl3 is confirmed by the reactivity inherent to these functional groups. The expected reactions take place but are limited by the formation of a three dimensional network resulting in insoluble compounds. Thus, a modified polyisoprene (n=15) loses only 60% of its chlorine by heating to 130° C in xylene solution in presence of finely dispersed sodium. It is difficult to eliminate the remaining chlorine because the radicals formed by the —CCl3 groups produce crosslinking. Phenyllithium produces similar effects to those of sodium, in addition a certain number of phenyl groups are added and result in bands found at 1,495–1,580 cm−1. The presence of hydroxyl groups is also verified by reaction with acetyl chloride. Bifunctional reagents such as adipoyl dichloride or hexamethylene diisocyanate produce crosslinking reactions which become evident by rapidly increasing insolubility.
Studies of the Hard Rubber Reaction. I. Heat of Reaction
Authors: Bhaumik M. L. , Banerjee D. , Sircar Anil K.
Published: February 2011

A method for the determination of the heat of the hard-rubber reaction by the application of differential thermal analysis is reported. The heat of reaction was determined with stocks containing different rubber/sulfur ratios and also with a 68/32 stock, preheated to contain different amounts of combined sulfur. Heat evolution is observed first with samples containing about 7 per cent sulfur and therefrom the amount of heat evolved shows a nearly linear increase up to 30 per cent sulfur. With increasing combined sulfur in the 68/32 stock, the quantity of exothermic heat gradually diminishes; so also does the temperature of initiation, i.e., the temperature at which heat evolution appears to begin. Initiation of the exothermic reaction appears to be a function of composition and temperature of the mass. An increase in the rate of reaction was observed when the composition reached 0.5 g-atom of sulfur per isoprene unit. An endothermic dehydrogenation reaction is observed at the end of the hard-rubber reaction. This, however, does not affect the determination of exothermic heat, because there is similar dehydrogenation taking place in the reference material (ebonite) which almost balances this heat loss. The final product has a lower sulfur content due to loss of sulfur as hydrogen sulfide.
A Molecular Theory of Filler Reinforcement Based upon the Conception of Internal Deformation (A Rough Approximation of the Internal Deformation)
Authors: Sato Yoshiyasu , Furukawa Junji
Published: February 2011

A molecular theory is presented in this paper which gives a method of analysis for the mechanical properties of filler-reinforced elastomers, based upon the concept of the internal deformation and the statistical theory of rubberlike elasticity. By using a suitable model and a few new concepts a proper analysis for such a heterogeneous system is obtained. From the theory the internal mechanism of filler reinforcement is understood. It is made clear that reinforcement consists of three effects: the volume effect, the surface effect, and the cavitation effect. From the theory, formulae for the tension, swelling tension, Young's moduli, local stress distribution, strain birefreingence, condition for swelling equilibrium, and so on are derived. It has long been recognized that rubbery substances and plastic materials are reinforced by incorporation of suitable powdery substances (reinforcing fillers) which improve their mechanical properties such as elastic modulus, hardness, stiffness, resilience, solvent resistance, plastic viscosity, tensile strength, tear resistance, etc. Although numerous attempts have been made to clarify and systematize the internal mechanism of filler reinforcement, there is at present no distinct picture of the mechanism, much less a satisfactory theoretical treatment of the phenomena.
Spectrophotometry and Chromatography for Identification of Antioxidants and Accelerators in Rubber Mixtures
Authors: Fiorenza A. , Bonomi G. , Piacentini R.
Published: February 2011

The difficulties encountered in the identification of antioxidants and accelerators in rubber mixtures are reviewed. A method of column chromatographic separation of components contained in the mixture extracts is discussed. The identification of the principal ingredients is achieved by means of ultraviolet and infrared spectrophotometry utilizing mixtures containing different antioxidants. Various spectra are presented, produced by both types of spectrophotometry, illustrating the efficiency of the method. The method could also be used to identify certain components of plastic material extracts.
Vulcanizing Efficiency during the Scorch Period
Authors: Gerke Roscoe H.
Published: February 2011

Values of vulcanizing efficiency, Ci/Si for different rubber compounds have been determined by extrapolating curves of crosslinking (or stress) versus percentage combined sulfur to the combined sulfur axis. The values Ci/Si are corrected for sulfur content of the ingredients, rubber or carbon black. For Hevea vulcanizates determination of the ratio Ci/Si gave values of zero or infinity. SBR vulcanizates also gave values of zero or infinity. For a polybutadiene vulcanizate Ci/Si it was found to be zero. A TMTD Hevea stock showed neither detectable crosslinks nor combined sulfur during the first ten minutes of heating but when sulfur started to combine Ci/Si was found to be infinity.
Crosslinking Reactions of Carboxylic Elastomers
Authors: Brown H. P.
Published: February 2011

Carboxyl groups in elastomer molecules have been shown to contribute to the crosslinking or joining of these molecules through hydrogen bonding, salt formation, reaction with diepoxides or polyepoxides including epoxy resins, reaction with diamines or polyamines, esterification with di- or poly-hydric alcohols, reaction with carbodiimides, reaction with polyimines, and by reaction with polyisocyanates. Each of these reactions alone may produce useful crosslinkages. Or, they may be used in conjunction with crosslinking reactions operating in other parts of the molecule such as sulfur or peroxide vulcanization. This has been particularly true of salt formation, especially through the use of zinc oxide, with sulfur vulcanizarions. The carboxyl groups in some instances may be generated during the crosslinking reaction. Thus polyethylacrylate may be crosslinked with hexamethylene diamine, barium hydroxide and similar reagents. Many of the reactions of the carboxyl groups in elastomers are quite rapid. For some purposes such as surface toughening of elastomer films, this may be quite useful. For others such as the vulcanization of carboxylic elastomers with zinc oxide or with recipes containing zinc oxide, this may be objectionable because of the scorchiness of the stocks. The scorchiness of vulcanizates of carboxylic elastomers involving zinc oxide may be controlled with organic acid additives or by the use of zinc oxide coated with less reactive materials such as zinc sulfide or zinc phosphate. The speed of reaction of epoxides with carboxyl containing polymers is influenced by the structure of the epoxide. The ease with which carbodiimides induce crosslinkage is dependent upon the structure of the carbodiimide.
Vinylpyridine Rubber (PBR)-Filler Interactions. II.
Authors: Brucksch W. F.
Published: February 2011

This paper describes some reactions of vinylpyridine rubber with fillers. The work was done to learn if there is a chemical basis for the superior abrasion resistance of pyridine rubber treads. The results show that chemical factors are important when rubber-to-filler interaction is involved. The copolymerized pyridine groups of the rubber are absorbed readily onto the filler surface, especially when the pyridines are modified by complex formation with certain zinc salts or by conversion to pyridinium cation. Multiple adsorption generates a network. Those qualities associated with reinforcement are enhanced: viscosity (carbon black “stiffening”), “bound” rubber, electrical resistivity, modulus and resistance to tearing and to abrasion. The network bonds are, however, temperature dependent and can be erased by heating to 100° C. Adsorption of modified pyridines onto filler is like the mordant dyeing of fabrics. The pyridinium compound acts like a color “lake” adsorbed onto carbon black. Adsorption-bonding can be used to generate a portion of the modulus in sulfur-cured treads. For the same modulus, less sulfur is required, with a corresponding improvement in heat-aging.
Introduction to the Molecular Viscoelastic Theory of Polymers and Its Applications
Authors: Peticolas Warner L.
Published: February 2011

In summation, it can be said that the relation between the molecular characteristics of polymers, such as molecular weight, branching and their corresponding distribution, and the rheological properties of polymers can now be given with remarkable success, though much work remains to be done and refinements are badly needed. These relationships should help permit the design of polymers with exactly the right molecular weight and branching distribution to meet specific end-use requirements. It is hoped that the present review will be of use to rheologists seeking to design polymers for certain end-use specifications as well as to stimulate further research in this area.
Application of Finite Elastic Theory to the Behavior of Rubberlike Materials
Authors: Blatz Paul J.
Published: February 2011

A brief review of the theory of finite elasticity is presented. The theory is applied to the characterization of the mechanical response parameters of a polyurethan foam. The incorporation of compressibility and anisotropy effects into the strain energy function are discussed. An example of the behavior of a composite or filled foam is presented. Finally some of the problems associated with the molecular interpretation of mechanical parameters are discussed.
Polyolefin Elastomers
Authors: Natta G. , Crespi G. , Valvassori A. , Sartori G.
Published: February 2011

The new processes of anionic co-ordinated polymerization have permitted the synthesis of new polymers which are of interest as plastics, fibers, and elastomers. Among these last, the ethylene-propylene rubbers are particularly interesting for the future of the rubber industry. In fact these elastomers are prepared from low-cost raw materials (ethylene and propylene) and show good mechanical and elastic properties as well as excellent resistance to aging.
The Friction of Polymers on Ice
Authors: Gnüeich W. , Grosch K. A.
Published: February 2011

The paper describes friction experiments on smooth icy surfaces at various temperatures. Speed and temperature variations for NR gum rubber shows that in principle the WLF transformation can be applied to friction on ice, and friction—temperature curves may be interpreted as being part of the friction master curve on smooth solid surfaces. Very near the melting point the friction decreases rapidly for all polymers, and this appears to be associated with changes in the nature of the icy surface. At low temperatures, the friction—temperature curves do not only agree in shape with curves obtained on glass but reach similar values in magnitude also. Black and oil extension effects are also similar to those expected from friction experiments on other surfaces. The blending of polymers, either in the gum state or filled with carbon black, broadens the region of high friction, enveloping the friction curves of the two polymers making up the blend. Depending on the temperature region, either one of the constituents of the blend dominates the friction behavior. It is instructive to speculate on the relevance of these experiments to winter tire performance. It is obvious that the very clean polished smooth ice track obtained only under great difficulty even in the laboratory is not realizable in practice, so that the ice on which tires operate is in every case contaminated with either snow, water, or dirt. In this case the coefficient of friction drops drastically, as is demonstrated in Figure 11. Nevertheless it is easily shown that compound effects do exist in tire skid measurements on ice. It is generally observed that NR-based compounds have a higher skid resistance on ice than SBR-based ones. This ranking is also observed in all experiments described in this paper and is explainable because of the position of the friction master curve. Even if practical speeds, as they occur in tire usage, are considered, it is easily demonstrable that the shift of the master curve towards lower temperatures is insufficient to have a real impact on compound relations. It is in any case minimized by the fact that, at high sliding speeds, the simultaneously occurring temperature rise in the interface tends to cancel any velocity shift in the master curve. On ice the temperature rise cannot exceed 0°C, so that only a very small band of the master curve is in operation. In this band, NR is near its maximum, SBR has exceeded its maximum value, and BR has not reached it.
Influence of Carbon Black on Process-Ability of Rubber Stocks. I. Bound Rubber Formation
Authors: Cotten G. R.
Published: February 2011

1. A direct correlation between bound rubber content and molecular weight of soluble polymer was found for a wide range of carbon black samples and processing conditions in SBR. 2. No significant polymer degradation occurred during the ineorporation of carbon black into SBR rubber. 3. A theory was proposed to explain the observed changes in viscosity and extrusion shrinkage of rubber stocks. This theory is based on the concept of occluded rubber which is rich in high molecular weight polymer and behaves as a part of filler volume during viscous flow.
Reinforcement of Silicone Rubber by Particulate Silica
Authors: Boonstra B. B. , Cochrane H. , Dánnenberg E. M.
Published: February 2011

The interaction between fumed silica and silicone elastomer after various treatments of the silica surface has been investigated. The effect of the treatments was determined by measuring bound rubber, an interaction coefficient by means of the oscillating disk rheometer, the mechanical properties of the vulcanizates, the morphology of the silica aggregates, and the use of an hydroxyl-terminated silicone rubber. The results indicated that the interaction is much more intensive than in carbon black-hydrocarbon rubber systems. This is demonstrated by much higher bound rubber values (by a factor of 2–3) and a higher interaction coefficient. It is shown that the major effect on this interaction coefficient is the specific interaction by hydrogen bonding, between silica surface silanol groups and the polydimethylsiloxane chain. In this bonding the isolated hydroxyl groups should play the major part. Partial inactivation of these isolated silanol groups leads to improved strength but lower modulus. Maximum inactivation of the surface hydroxyl groups leads to soft compounds with lower tensile strengths and moduli, as well as very low bound rubber. Replacement of surface hydroxyl groups by vinyldimethylsilyl groups did not have the expected activating effect. Apparently the attached vinyldimethylsilyl groups do not form crosslinks with the elastomer chains, so that the overall result of the presence of these groups on the silica surface is a weakening of the interaction with the silicone rubber chains, although to a lesser degree than in the case of trimethylsilyl groups. The interaction between filler surface and polysiloxane can be maximizedby the use of a hydroxyl-terminated elastomer. The terminal groups will react with the silica surface so strongly that the particles act as crosslinks after proper heat treatment and a crosslinked polymer is obtained with a tensile strength of the same level as a peroxide-crosslinked vulcanizate but with higher compression set. At the temperature of the compression set test (175°C) the bonds apparently rearrange so that the permanent deformation is practically 100%. Quantitative data have been presented which prove that breakdown of silica aggregates does occur during mixing in silicone rubber on a two-roll mill.
Strain Dependence of the Glass Transition Point in Chlorinated Polyethylene Vulcanizates
Authors: Naoki M. , Nose T.
Published: February 2011

The experimental glass transition temperature observed as the inflection point in a certain physical quantity, Tgapp, changes not only with glass-forming conditions but also with the variables observed. Moreover the change of Tgapp with extension largely depends on the variables observed. These results indicate that Tgapp as determined by measurement of a certain physical quantity is not necessarily a direct reflection of the molecular mobility.
Mechanistic Studies on the Photooxidation of Commercial Polybutadiene
Authors: Beavan S. W. , Phillips D.
Published: February 2011

Products from both the thermal and photooxidation of polybutadiene have been studied using various analytical techniques such as infrared and ultraviolet spectroscopy, gas—liquid chromatography, phosphorescence emission, and phosphorescence excitation spectroscopy. Analyses have allowed a plausible mechanism to be formulated for the photooxidation of this polymer, consistent with all the observed physical and chemical changes. Both photo- and thermal oxidative polymer degradation initially result in the formation of α,β-unsaturated carbonyls which, under photo-degrading conditions, are subsequently photolysed to yield the observed final products.