bluuebunny/crossref_metadata_2025 huggingface dataset:
Degradation of Rubber by Chemical Agents in Solution
Authors: Foxley G. H.
Published: February 2011

It is clear that the subject of polymer degradation by chemical agents is an active branch of polymer chemistry. This is reflected in the large number of patents applying to polymer degradation and no attempt has been made to include every appropriate patent. Much of the comparative work is based on equal weights, rather than equal numbers of molecules, so that the true comparisons of the efficiency of peptizers are often difficult. It has been shown that polymer degradation can proceed via several mechanisms all of which involve free radicals and the main points can be summarized as follows :— In solutions at low temperatures the initiatory free radicals come from the added peptizer such as benzoyl peroxide or bis-azoisobutyronitrile. Although oxygen accelerates the reaction, it is not essential, and there is appreciable degradation in the absence of oxygen. Thiols are active only when oxygen is present even at high temperature. This is somewhat surprising, since the rubber radicals produced by thermal scission should be just as active as those produced by mastication and be capable of reaction with thiols, and serves to emphasize the importance of the role of oxygen in peptization by thiols and disulfides. Oxygen is also necessary for degradation by redox systems and in its absence structurizing takes place. The lack of work on triphenyl methane derivatives is somewhat surprising in view of the ease with which they undergo homolysis to give free radicals. However, it is not sufficient to introduce any type of free radical and expect degradation: stabilized free radicals are the best peptizers, unstable radicals can add to olefinic bonds and cause crosslinking rather than chain scission. Squalene has been used as a model compound for the study of the reactions of natural rubber with free radicals in a similar manner to the use of methylcyclohexene as a model compound for oxidation studies. This review forms part of a dissertation submitted in partial fulfillment of the requirements for the London University M.Sc. (External) Examination.
Recent Developments in Synthetic Rubber Latex
Authors: Howland L. H. , Brown R. W.
Published: February 2011

Progress has proceeded at a good rate since the close of the Government Program in the spring of 1955. Improved latexes have been made, and the technology of manufacture and of application has advanced. Also progress has been made in fundamental latex research. Some of the newer latexes representing the more important advances are those involving functonal groups derived from the use of unsaturated monomers such as those containing amino groups and carboxy groups in the polymerization system, those from solid rubbers by the solvent emulsion technique, and those of higher solids content including the agglomerated latexes giving 68 per cent minimum solids at low viscosity. Some of the applications of greatest growth are : 1. Carpet backing involving both sulfur curing and so-called self-curing (noncured) elastomer latexes. The latter obtain strength from polar groups including functional (carboxyl) groups and/or fairly high styrene content. 2. Foam sponge backed carpets. In 1954 it was suggested that synthetic rubber latexes would have a permanent place in our economy. This has now come to pass, and natural latex is decreasing in volume compared to total synthetic rubber latex consumption. It now appears that by forming a latex from cis polyisoprene (synthetic natural rubber) and adding it to our list of latexes, that our country could probably become independent of the natural product.
Fluorine-Containing Elastomers
Authors: Montermoso J. C.
Published: February 2011

Fluoroprene, the first fluorine-containing elastomer, was developed by E. I. du Pont de Nemours … Company and reported by Mochel and others in 1948. However, intensive research to develop specialty rubbers from fluorocarbons was not started until the early 1950's. At the time, there was an urgent military need for fuel and chemical resistant rubbers for service under extremely low temperatures. Consequently, most of the fluorine-containing elastomers were the result of research conducted or sponsored by the Department of Defense. Army experiences in the Aleutians during World War II and in several task force operations in the Arctic regions showed, among others, that fuel hoses became brittle and cracked. Gaskets failed to function. On shipboard, the Navy was experiencing similar difficulties with rubber items. The Air Force, on the other hand, was being plagued with an epidemic of fuel leakage on many of its aircraft. The extraction of the plasticizers from the nitrile rubber compounds and the low temperature of the environment caused shrinkage of the seals and gaskets resulting in leakage of fuels. Obviously, a solution to these problems was to develop new fuel resistant rubbers which would be inherently flexible at extremely low temperatures.
Copolymerization of Butadiene and Isoprene through Use of Complex Organometallic Catalysts
Authors: Bresler L. S. , Dolgoplosk B. A. , Kolechkova M. F. , Kropacheva E. N.
Published: February 2011

Processes were investigated for the copolymerization of butadiene and isoprene, with the catalyst systems: aluminum triisobutyl/TiCl4 and aluminum diisobutyl chloride/cobalt chloride, complexed with ethyl alcohol. From study of the properties of the resulting polymers, and of butadiene/ isoprene homopolymer mixtures, it was established that in the presence of the cited catalysts, genuine copolymers were in fact obtained from the mixtures of isoprene and butadiene. Constants were determined for the copolymerization of butadiene and isoprene, in presence of the indicated catalysts, by tracer techniques.
Accelerated Thermomechanical Testing of Vulcanizates
Authors: Briggs G. J. , Edwards D. C. , Storey E. B.
Published: February 2011

The use of simple mechanical tests, conducted in an environment of rapidly changing temperature, proves to be a valuable approach to the preliminary study of rubber compositions. The differential strain test in particular is a most useful and convenient scanning procedure, allowing the estimation of basic quantities and the assessment of the general physical character of experimental vulcanizates. The test serves to identify types and regions of unusual behavior, which can then be pursued if desired by methods appropriate to the case. Where the careful study of particular questions requires the application of more refined and specialized techniques, these simple mechanical procedures, requiring little time and material, can contribute greatly to intelligent experimental design.
Analytical Chemistry of Plastics. XIX. Analysis of Rubberlike Mixed Polyurethans
Authors: Schröder Elisabeth
Published: February 2011

Polyester urethans, the most important class of rubbery mixed polyurethans, can be recognized by their nitrogen-containing, neutral-to weakly-acid pyrolysis gases in conjunction with their ease of saponification. Also the detection quoted by Swann using p-dimethylaminobenzaldehyde can be recommended for their identification. In view of the multiplicity of possible methods of forming polyester urethans it appears, however, more important from the standpoint of quantitative analysis to provide for identification of the most important components as well as allocation to a definite raw material group. Detection of dicarboxylic acids.—The detection of carboxyl groups by way of hydroxamic acids has already been referred to. This detection, which is always positive for every dicarboxylic acid and is of low specificity, has to be supplemented by special detection methods. Of these we may name:
Flexcracking of Polymers
Authors: Akkerman F. H. D.
Published: February 2011

Accurate measurement of several types of fatigue failure in polymers was obtained with a flexing machine equipped with an automatic camera. The technique is described at length. Observations made include that an antiozonant interferes with crack initiation, that a crack may well start under the surface, and that in the growth of a crack the elastic force is equivalent to the hysteretic force. Several photographs show aspects of crack initiation.
The Use of Rubber Models as a Stress Aid
Authors: Pope A. W.
Published: February 2011

During the design of a new diesel engine crankcase, it was thought that it would be possible to get a measure of the effectiveness of various rib shapes and positions by using a scale rubber model. Silicon rubber (made by I.C.I.) was chosen, as this could be cast easily and would faithfully follow any pattern. As it proved difficult to make a negative pattern of a section of a crankcase, a normal wooden pattern was made and then rubber cast around it. This made a rubber mold (see Figure 1 ), which was used, after coating with a separating agent such as “Vaseline”, to cast a final rubber model. This is shown in Figure 2. Strips of paper were placed between the model and the board (B) to which it was glued so that there was only attachment where there are bolts in the actual engine.
Thermostability of Sulfenamide Accelerators in Tire Compounds
Authors: Kleeman W. , Erben G.
Published: February 2011

The laboratory-type decomposition isotherms plotted by the authors have shown that in all the investigated commercial-type sulfenamide accelerators, dissociation already occurs at 120° C. Within the range of the required mixing times, 140° C can be regarded almost generally as the critical temperature. As shown by technological investigations, at 140° C and higher, there is definitely a marked effect on processing properties, and on the vulcanization behavior of the compounds. The results of the investigation clearly demonstrate, once again, that when compounding temperatures are going to exceed 140° C, it is necessary to mix in the sulfenamide accelerators in a second stage at lower temperatures, preferably below 100° C. Even when the accelerators are incorporated on a mill, immediately after the internal mixer is discharged, a dissociation of the sulfenamide accelerator must be reckoned with if the compound cannot be sufficiently cooled.
The Fraction of Effective Sulfur Crosslinking in SBR Vulcanizates
Authors: Meltzer T. H. , Dermody W. J. , Tobolsky A. V.
Published: February 2011

Shear modulus measurements as a function of temperature have been made for SBR vulcanized with sulfur in amounts between 6 and 34% of the recipe. The shape of the modulus-temperature curves are typical of crosslinked amorphous polymers and there is a consistent displacement of the curves toward higher temperatures as the percentage of sulfur in the mixture is increased. The rubbery plateau modulus also increases with increasing sulfur, and from its magnitude the concentration of crosslinks is computed. The ratio of crosslinks to total sulfur atoms is below 0.20 in all cases. The results lend support to the conclusions of Bateman and of Bloomfield that a high proportion of cyclic structures is formed during sulfur vulcanization.
Evaluation of Crosslinking Coagents in Ethylene-Propylene Rubber
Authors: Lenas L. P.
Published: February 2011

Ethylene-propylene rubber (EPR), a saturated elastomer, is usually vulcanized by a peroxide-sulfur curing system. However, several disadvantages associated with this system—undesirable odor for some applications, narrow curing range, and poor strength obtained with mineral fillers—emphasize the need for other reactive chemicals as crosslinking coagents for EPR. Certain polyfunctional monomers such as ethylene dimethacrylate, and polyfunctional polymers such as 1,2-polybutadiene were promising crosslinking coagents for EPR. When used in place of sulfur, they decrease peroxide requirements of moderately filled EPR compounds. They also impart higher states of cure, improve the cure cycle, and decrease odor. The coagents are much superior to sulfur in mineral-filled EPR compounds where, in addition to increasing the crosslinking efficiency, they also improve the wetting of the filler particles by the rubber. However, in highly loaded (carbon black and oil) EPR formulations, the superiority of the peroxide-coagent system is mainly due to the ability to replace sulfur and, consequently, to improve odor.
A New Type of Tackmeter
Authors: Bussemaker O. K. F. , van Beek W. V. C.
Published: February 2011

A new type of tackmeter is described. Strips of the material to be tested are used for tack measurements. The instrument compresses and separates the strips under conditions which can be arbitrarily selected. The tackmeter is of rugged design for simple handling and ease of operation. The test results are recorded on a chart, enabling easy reading of the results. A description of the tackmeter and the testing procedure is given. The accuracy of the measurement is briefly discussed. Among the factors affecting the measurement are the thickness of the sample, compression conditions and aging of the surface. Some test results obtained with factory-made plies and compounds with varying black loadings are given.
Thermomechanical Characterization of the Molecular Weight of Linear Polymers Exemplified by Natural Rubber
Authors: Teitelbaum B. Ya , Gubanov K. F.
Published: February 2011

In the previous work of Kargin and Slonimskii and that of Kargin and Sogolov who studied the behavior of polymers over a wide range of temperature, it was shown that the shape of thermomechanical curves depends on magnitude of molecular weight of the polymers. As a result of investigation of theory and actual experimental studies in which polyisobutylene was employed, it was demonstrated that molecular weight could be estimated on the basis of thermomechanical properties. This suggested a relationship between the magnitude of molecular weight M found from the thermomechanical curves and that which was determined from glass temperatures Tg and fluid temperatures Tf. For practical use of this relationship, it is necessary to know the magnitude of the segments and two empirical constants. These values can be found by calculation of molecular weights of three different fractions of the polymer. This can be accomplished experimentally by any independent method. Once these magnitudes are determined, it is necessary to find, by means of the thermomechanical curve, the values Tg and Tf, in order to calculate the molecular weight of any sample of the same polymer. Because of the low degree of accuracy of determination of these values, and because of the peculiar differences, the reliability of the calculated molecular weight cannot be great, especially since the equation utilizes the logarithm of the molecular weight figure and not the molecular weight itself. Apparently the graphic solution is simpler than analytical methods: by means of the data of thermomechanical studies for various fractions of known molecular weights it is possible to graph the dependence of M or log Mon Tf−Tg. From what has been said, it is evident that we may use the demonstrated method only for polymers of high elasticity, and furthermore, only for those fractions in which Tf−Tg is greater than zero.
On Testing Rubber
Authors: Juve A. E.
Published: February 2011

Measurements are basic to all natural sciences, in fact some say that science is measurement. Whether it is the measurement of the temperature on the moon or the hysteresis properties of a rubber compound, the measurements are intended to give us accurate data with which to proceed further in our understanding of nature. Measurements and analyses are essential in every stage of rubber science and technology from the synthesis of a new rubber chemical to measurements of performance of some complex product such as a tire in service. The all-pervading role of measurements is frequently not appreciated, but a simple observation which each of us can make will demonstrate this fact. A cursory examination of the slides presented at this and other Division of Rubber Chemistry meetings will show that at least 95% of them contain the results of physical or chemical tests required to demonstrate, illustrate or prove a point the speaker is attempting to make. Furthermore, many of the papers will be concerned solely with a new test method or method of analysis. Although as a compounder my work was only incidentally involved with testing, the subject of testing has been a most absorbing interest of mine and it seemed that a discussion of some aspects of it would be acceptable for this lecture. A rough distinction can be made between those tests involved with the fundamental science of rubber as a primary aim and those involved with the engineering practice of rubber technology, although there is an inevitable overlapping. My concern here will be with the latter group and, in general, with those methods which have been standardized by Committee D-11 of ASTM. My central theme will be that too much testing is done, that many of the methods are inadequate, that many are inadequately understood by the users and inadequate analysis and interpretation are made of the data obtained. In an attempt to brighten the picture a little, I will conclude by discussing some new methods which appear to be decided improvements, both from performance and in being adequate in respect to being easily understood by most users. What I have to say will be somewhat critical of the methods used and sympathetically critical of the people who use them. At the start I should point out that criticism of the methods is not a criticism of Committee D-11 of ASTM. It should be realized that D-11 almost invariably standardizes methods which are fairly widely used in the industry and for which a need for standarization is expressed by the industry. The Committee rarely develops new methods, although it can be said that in the process of standardization, methods are usually improved. One of the more important purposes of standardization is to formulate methods so that different laboratories will obtain reasonably reproducible values without which chaos would result.
Experimental Findings on the Abnormal Freezing Point Depression of Swelled Cured Natural Rubber
Authors: Butenuth G. , Westlinning H.
Published: February 2011

The method of Kuhn and coworkers for the determination of crosslink density for swelled cured rubber was applied to unfilled peroxide- and sulfur-cured samples. Comparison with other methods confirms the new method. Experimental data for a number of filled samples is presented together with the mesh size of the network determined by the method of Kuhn.
Service-Induced Diffusion and Nodule Formation in Rubber Stocks
Authors: Smith R. W. , Black A. L.
Published: February 2011

Diffusion of materials within a rubber compound caused by temperature gradients may cause nucleation and growth of crystals in favorable sites. The rubber may or may not be affected by this process, but if it is affected, a dense area termed a nodule results. Zinc stearate is the prime agent responsible for forming nodules in typical tread compounds. After the formation of a localized concentration of the stearate, crosslinking conditions are favorable and this proceeds with the infusion of sulfur. Conditions favorable to nodule formation are those conditions favoring diffusion, i.e., prime temperature gradients, “soft” compounds, solubility effects and undoubtedly dynamic mechanical stress.
Thermomechanical Studies of Amorphous and Crystalline Polymers
Authors: Sidorovich A. V. , Kuvshinskii E. V.
Published: February 2011

A thermomechanieal study has been made of the softening of crystalline polymers during uniform, uniaxial stretch and also of the effect of the rate of heating upon the softening of amorphous polymers. The effect of the tensile force on the thermomechanical behavior of various polymers has been followed over the range 20 to 100 kg/cm2 and within wide temperature limits ( −150° to 250°). Ribbons 50 mm long, 2 to 4 mm wide and 0.05 to 0.5 mm thick served as specimens. Of the crystalline polymers the study included: isotactic polypropylene, polyethylene, polytetrafluoroethylene and polyethyleneterephthalate; of the amorphous: polyethyleneterephthalate and styrene-butadiene SKS-80 copolymer. The simplest thermomechanical curves were those of the amorphous linear isotropic polymers. The curves are characterized by a point of inflexion—abrupt increase in deformation on reaching the softening point. The thermomechanical curves of crystalline polymers are more complicated and are characterized by three differing regions of creep: below the glass, temperature, cold flow and the beginning of melting.
Molecular Structure and Properties of Polybutadiene Rubbers
Authors: Blümel H.
Published: February 2011

A discussion of the development, present day applications, and the advantages of polybutadienes are presented. The variations of an over-all concept in products obtained through different preparations and having various molecular structures as well as differing service and technological properties were made the starting point for the present investigations. Section 2 provides a review of the basic characteristics of the most important processes for preparing polybutadiene and the associated structural or compositional characteristics. Fourteen typical polybutadienes encompassing the entire range of polybutadienes are compared to cold rubber and natural rubber with respect to their most importance analytical and polymer values corresponding to their arrangement into preparation groups. The correlations between the technological properties of the raw rubbers, of the compounds, including the mixing behavior, and the vulcanizates on the one hand and the molecular structure composition of the rubbers upon which they are based, on the other, are discussed using detailed synopses in Sections 3 and 4. In doing this, it was important to see the principal features of the different polybutadienes compared to one another, effects of the structural characteristics and of additives on the properties of the raw rubbers, compounds, and vulcanizates, as well as the differences encountered as compared to polymers which are considered most important for use in blends (cold SBR and natural rubber). Finally, in Section 5, in summary form, the effects were treated of the individually appearing structural and compositional factors in the initial polymers on the service and technological properties of the raw rubbers, compounds, and vulcanizates.
The Viscurometer—An Instrument to Assess Processing Characteristics
Authors: Juve A. E. , Karper P. W. , Schroyer L. O. , Veith A. G.
Published: February 2011

This paper describes an apparatus that measures three important rubber processing characteristics—the compounded viscosity, the scorch time and the time to optimum cure. The apparatus is called a Viscurometer and consists of a heated die chamber and a drive mechanism to rotate a biconical rotor in an oscillatory manner through a fixed arc of ±6°. A strain gage torque pickup is mounted as an integral part of the drive shaft and the torque to impose the strain of ±6° (35% shear strain) is measured. The frequency of this oscillation is 2 per minute. A torque vs. time trace is recorded on a strip chart recorder. Data in graphical form are presented to show that the compounded viscosity of NR and SBR stocks correlates well with typical Mooney viscosity values. The scorch time, as measured with the Viscurometer, also correlates well with Mooney scorch values. The apparatus can be used to predict optimum cure for typical production SBR and NR stocks with a one standard deviation precision of ±2 minutes. The apparatus can also be used to predict the cured modulus at full cure (or any other percentage) under some conditions. This use of the Viscurometer is, however, more complex than its use to predict the previously mentioned processing parameters. The complexity of this use is illustrated for some typical NR and SBR stocks.
Vulcanization of Elastomers. 45. Experiments to Determine the Huggins Interaction Parameter
Authors: Hummel K.
Published: February 2011

A new method is described for determining the Huggins interaction parameter, µ. It is characterized by the measurement of the equilibrium swelling of two completely reacted vulcanizates for which the initial composition is known. The method gives correct results only under definite assumptions which are explained for the case of natural rubber crosslinked by dicumyl peroxide. Its applicability is demonstrated for the system natural rubber/benzene at 25° C; the results, however, scatter considerably.
Quantitative Relationship between Mineral Oil Composition and Elastomer-Extender Interaction Parameter
Authors: Bruzzone M. , Modini G.
Published: February 2011

Among the synthetic rubbers, the styrene-butadiene elastomers (SBR) extended with oil have grown more and more important in these last years. These elastomers are obtained by masterbatching an SBR latex of high Mooney viscosity with a mineral oil before coagulation, the oil content normally ranging between 37.5% and 50%. The mineral oil can be classified as predominantly paraffinic, naphthenic, or aromatic according to the ratio of carbon atoms involved in the paraffinic, naphthenic, or aromatic structures. The oil composition greatly affects both the processing and the final-product properties of the extended elastomer. It is well known, for instance, that SBR extended with paraffinic oil is more critical in processing than when extended with naphthenic or aromatic oils, and, on the other hand, that SBR extended with paraffinic oil shows better resistance to the discoloration caused by exposure to light. Leaving the long list of the effects on elastomeric properties of oil composition to the many papers existing on this subject, we prefer to deal here with a very important subject not very much studied on any quantitative basis until now. The oil composition affects many characteristics of the polymer because it brings controllable variation to the physical-chemical interaction between the polymer and the extender, measurable by the Flory-Huggins interaction parameter and strictly related to the more commonly known compatibility meaning. This work deals with the quantitative relationship between the composition of various mineral oils (determined by a well-known method) and their interaction parameters with SBR which greatly affect the main properties of the extended elastomer and which we determine by a swelling measurement of the crosslinked elastomer.
The Elasticity of Rubber-Bitumen Binders for Use in Roads
Authors: de Merlier Jacqueline , Leveque J. , Curchod J.
Published: February 2011

The authors have first described test methods used, on the one part, to determine, in a simple way, the elastic recovery of binders after deformation, and on the other, to characterize accurately the state of degradation of the rubber within the bitumen by assessing the molecular weight of the dispersed polymer. Analysis and interpretation of results have stressed: (a) the effect of the molecular weight of crude natural rubber on the elastic recovery of bitumen-rubber blends; (b) the effect of the way in which bitumen-crude natural rubber blends are prepared on their elastic properties and (c) the effect of the nature of synthetic elastomers on the elasticity of bitumen blends.
Effect of Peperidine on Rubber Solutions
Authors: Soininen A. , Bäsk W. , Pehu-Lehtonen A-L.
Published: February 2011

In the experiments which have been described, the viscosity measurement served as an indicator to establish the amount of piperidine required for a substantial viscosity reduction. The bend in the viscosity curves for the 5% crepe solutions occurred for a piperidine addition of about 3×10−5 moles. The quantity appears to be in stoichiometric relation to the rubber used. Therefore we come to the view of Meyer, that rubber exhibits associating, oxygen-containing groups. Accordingly, the strong effect of piperidine in lowering the viscosity is due to the action of this amine in splitting all the association bonds of the oxygen-containing groups in the rubber molecules. Not only the weak alcohol and keto bonds are concerned but also the strong carboxyl bonds. Infrared spectroscopy also has shown that Hevea rubber contains a rather large portion of such groups. These probably are first formed in the processing of the latex. It is quite possible that the rubber molecules associate with the help of carboxyl groups, as carboxylic acids generally do, and form the relatively stable dimer compound shown below with two hydrogen bonds:
Tetracyclosqualene and Its Bearing on the Structure of Cyclized Rubber
Authors: Golub Morton A. , Heller Jorge
Published: February 2011

Recently we reported that cyclized rubber consists of six-membered rings fused into predominantly bicyclic structures which are connected by methylene groups and/or uncyclized isoprene units. Each of the fused ring structures is presumed to contain a single tetra-, tri- or di-substituted double bond, the relative amounts of which are in the order, tetra- > tri- > di-substituted. The predominantly bicyclic structure was not rigorously established, but it was considered reasonable on the basis of a comparison of the nmr spectra of cyclized cis-polyisoprene and cyclized cis-poly (2-methyl-d3-1,3-butadiene-1,1-d2). However, although a predominantly monocyclic structure was clearly excluded, it was not possible to rule out a structure in which the average number of rings per fused segment (“cyclicity”) exceeds two and may even be as high as three. In an effort to determine this cyclicity more accurately, we now compare the nmr and ir spectra of cyclized cis- and trans-polyisoprenes with the corresponding spectra of tetracyclosqualene (TCS). The latter is known to have a structure consisting of two bicyclic segments connected by two methylene groups.
The Rheological Unit in a High Polymer under Continuous Shear
Authors: Mooney Melvin
Published: February 2011

In summarizing the situation regarding the structure and properties of high polymer rheological units, we can say that while some definite progress has been made, there are far more present opportunities in the field than past achievements.
Estimation, from Swelling, of the Structural Contribution of Chemical Reactions to the Vulcanization of Natural Rubber. Part I. General Method
Authors: Ellis Bryan , Welding G. N.
Published: February 2011

A procedure is described for estimating indirectly the contribution of vulcanization reactions to the build-up of network structure. This method is useful with technically important vulcanizing systems for which no direct method of estimation has been found. Errors of the theory of high elasticity are avoided by using published results, such as those of Moore and Watson of direct chemical estimates obtained with a special vulcanizing system that is chemically well understood. Reliance on the theories of end correction and swelling is also avoided by using published experimental relations. The method is applicable to any linear primary polymer of arbitrary molecular weight and any suitable swelling liquid, for which the required reference data have been obtained.
Estimation, from Swelling, of the Structural Contribution of Chemical Reactions to the Vulcanization of Natural Rubber. Part III. Restricted Method
Authors: Russell R. M. , Smith D. A. , Welding G. N.
Published: February 2011

A method is described whereby the structural contribution of vulcanizing reactions may be estimated graphically from measurements of the equilibrium volume fraction of rubber in a vulcanizate swollen in n-decanc at 25.0°. Use is made of the data of Moore and Watson represented in the form of a relation between (ρMc−1)vulc and υτ. The method is applicable with technically important vulcanizing systems for which no direct method of estimation is available, and is simpler than the previous method (Part I). The method is limited to natural rubber of fixed primary molecular weight, but the limitation avoids a large correction for free ends of chains. Suitable experimental techniques are described.
Viscous Flow and Flow Temperature of Polymers
Authors: Sogolova T. I. , Slonimskii G. L. , Kargin V. A.
Published: February 2011

In recent years, E. V. Kuvshinskii and colleagues have published a series of articles devoted to thermomechanical studies of polymers. Some of these, together with some interesting data, led to strange conclusions concerning the absence of flow in polyisobutylene, polystyrene, and polymethylmethacrylate in thermomechanical experiments and also to the uselessness of distinguishing between the viscous flow state development and determination of flow temperatures of polymers. Obviously feeling a weakness in their argument, the authors of these articles showed, at the same time, that their results “do not refute the possibility of using the data from thermomechanical studies for technological purposes, including the establishment of proper temperatures for processing polymeric materials” (Ref. 1, p. 1704). We have established the fact that the position taken by E. V. Kuvshinskii and associates, in which they deny the existence of the viscous flow state of polymers and characterize flow temperatures, is in sharp contradiction to the current thinking concerning mechanical properties and structure of polymers. Their position adds nothing to our knowledge of the properties of polymers. Furthermore, their position is dangerous, because it docs not contribute to the clarification of the various phenomena taking place during the flow of polymers. This leads to confusion.
Vulcanization. Part I. Fate of Curing System during the Sulfur Vulcanization of Natural Rubber Accelerated by Benzothiazole Derivatives
Authors: Campbell R. H. , Wise R. W.
Published: February 2011

Several investigators have proposed mechanisms for the delayed action sulfur vulcanization of rubbers which postulate that a number of intermediate compounds containing fragments of the accelerator are formed during the vulcanization cycle. Although a number of workers have measured the change in initial accelerator and sulfur concentration in the rubber during vulcanization, none have identified and determined the intermediate compounds which appear to be formed during vulcanization. The purpose of this paper is to first confirm the existence of these intermediates and subsequently to identify and quantitatively follow their concentrations throughout the vulcanization cycle. In our initial studies we have limited our investigations to natural rubber cured with sulfur and accelerated with (i) MBT (2-mercaptobenzothiazole), (ii) (MBTS)[2,2′-dithiobisbenzothiazole)], and (iii) 2-(4-morpholinothio)benzothiazole. In order to reduce the complexity of the system, other normally used additional curing agents, notably ZnO and stearic acid, have been deleted.
Vulcanization. Part IV. The Effects of Compounding Variables on the Nature of Rubber Networks
Authors: Coran A. Y.
Published: February 2011

It is generally accepted for sulfur vulcanizates of natural rubber that the crosslinks consist of monosulfidic and polysulfidic links between polymer chains. There is indication in the literature that the average number of sulfur atoms per crosslink decreases with an increasing ratio of accelerator concentration to sulfur concentration. Further work was needed and in Paper III of this series a rapid method for determining the relative proportions of monosulfidic and polysulfidic crosslinks was described. The method was based on solvent swelling measurements of thin film vulcanizates before and after a lithium aluminum hydride reduction. By using this method along with a newly developed method for measuring stress-relaxation in a Monsanto Oscillating Disk Rheometer, it is possible to determine the relative proportions of three types of crosslinks: those which are nonreducible, those which are reducible but not rapidly stress-relaxable and those which are reducible and rapidly stress-relaxable. It is assumed that the stress-relaxation is due to cleavage of some of the polysulfidic crosslinks, but not others (those of the type R—S—S—R). It was our purpose here to define network characteristics as a function of compounding variations. The networks were characterized in respect to the distributions of the types of crosslinks as well as the number of crosslinks. It is felt that the nature of the networks as measured on the microscale would be significantly reflected in gross properties; this should be borne out in future studies.
Vulcanization of Elastomers. 46. The Kinetics of Crosslinking
Authors: Scheele W. , Hillmer K.-H.
Published: February 2011

The present article represents a first contribution to the investigation of the crosslinking kinetics of 1,5-polyenes, with sulfur as the vulcanizing agent. It is principally concerned with working out the pertinent methodology, and hence is a report on our experience with the “Agfa Vulcameter” (also called the Bayer Vulcameter). Using as an example the zinc benzothiazolyl mercaptide (ZnMBT)/zine stearate accelerated vulcanization of natural rubber with sulfur, which in any case runs with practically no reversion at moderate temperatures, and thus permits an experimental determination of the crosslinking end-values, we were able to show that crosslinking can be described quantitatively and qualitatively with the help of an Agfa Vulcameter. It was proved that the same reaction order and the same rates are obtained, as when the static modulus is used as the criterion for crosslinking. The scientific and practical importance of the results are pointed out.
Identification of Elastomers by Gas Chromatography Applied to Pyroluzates
Authors: Fiorenza Aldo , Bonomi Giuseppe
Published: February 2011

The general principles on which gas chromatography is based are reviewed, followed by a discussion of partition chromatography in particular. Certain typos of detectors are described as well as columns and column heating systems. There follows a review of the analysis of polymers by means of gas-chromatography. The methods employed for the examination of elastomers are also described. Finally, the chromatograms of various elastomers and their mixtures are presented which were obtained by using different types of columns.
On the Plasticization of PVC by Polyisoprene SKN-40
Authors: Byl'ev V. A. , Voskresenskii V. A.
Published: February 2011

The authors investigated the process of plasticizing PVC by SKN-40 synthetic rubber in the mixing of the components in the solid phase on hot rolls. It is found that with the optimum conditions the components mix in any desired ratio to form uniform strong and transparent films, having sufficiently high resistance to gasoline and water. It is shown that the addition of 1% sulfur to the system considerably enhances the mechanical properties of the compositions and their water resistance.
Reinforcement of Butyl with Carbon Black. II. Thermally vs. Chemically Oxidized Blacks
Authors: Gessler A. M.
Published: February 2011

The effect of oxidized blacks on the stress-strain properties and bound-rubber content of butyl and SBR was discussed in the preceding paper. Oxidized blacks, when compared with similar untreated blacks, were shown to have a greatly increased reinforcing capacity in butyl. Oxygen functionality on carbon black, it was therefore concluded, is essential in butyl to produce the chemical reactivity which is required between polymer and black if high-order reinforcement is to be obtained. Oxygen functionality on carbon black, it was also demonstrated, is not only not required for enhanced reinforcement in SBR, but it is in fact a deterrent, because it exerts severe restraining effects on the cure of the resulting vulcanizates as well. These interesting results were proposed to provide qualitative but convincing evidence that carbon-polymer bonding, which we believe is requisite to reinforcement, is achieved by different mechanisms in butyl and SBR. In butyl, the unique sensitivity of the stress-strain curve to reinforcing effects was used to speculate on the disposition of carbon blacks in “filled” and reinforced vulcanizates, respectively. With oxidized blacks, reinforcement effects were pictured as stiffening effects which, starting with the gum vulcanizates, caused the stress-strain curve to be shifted without intrinsic changes in its shape. The resulting “reinforced gum,” it was suggested, derived its physical characteristics from the fact that carbon black was included in the vulcanized rubber network. With untreated blacks, in “filled” systems, carbon black was pictured as being enmeshed or entangled in an independently formed vulcanized rubber network. The stiffening effects in this case were attributed to viscous contributions arising from steric restrictions which the occluded carbon particles were thought to impose on both initial movements and the subsequent orientation of network chains when the sample was extended.
Ultimate Tensile Properties of Elastomers. II. Comparison of Failure Envelopes for Unfilled Vulcanizates
Authors: Smith Thor L.
Published: February 2011

The tensile stress-at-break σb (based on the initial cross-sectional area) and the corresponding ultimate extension ratio λb of unfilled vulcanizates of silicone, hydrofluorocarbon (Viton B), butyl (both sulfur-cured and resin-cured), and natural rubber were determined at many strain rates and temperatures; the latter ranged from slightly above the glass transition temperature Tg, up to a temperature somewhat below that at which chemical degradation affected the results. For each vulcanizate except natural rubber, data obtained over an extended temperature range superposed to give a time- and temperature-independent failure envelope on a plot of log (σb273/T) vs log (λb−1), where T is the test temperature in °K; for natural rubber, data obtained between 90° and 120° C superposed, but those at lower temperatures did not because of strain-induced crystallization. For each vulcanizate, data at elevated temperatures gave, or tended toward, a line of unit slope on a plot of log (λbσb273/T) vs log (λb−1), where λbσb is the breaking stress based on the cross-sectional area at the moment of rupture. The position of each line corresponded to the equilibrium modulus Ee derived from stress-strain curves. Failure envelopes previously obtained for two styrene—butadiene vulcanizates, which had different crosslink densities, superposed to give a master failure envelope on a plot of log (λbσb273/T) vs logEe(λb−1). On this type of plot, failure envelopes for all the vulcanizates except silicone and natural rubber were found to be essentially identical. At a given value of λbσb, silicone had a smaller λbλb and natural rubber a somewhat larger λbλb than the vulcanizates of the three other rubbery polymers.
Molecular Theory for the Tensile Strength of Gum Elastomers
Authors: Bueche F. , Halpin J. C.
Published: February 2011

The tensile strength and ultimate elongation properties of any given amorphous elastomer can be described by a characteristic failure curve. It is shown in this paper that the failure curve can be predicted from a knowledge of the creep curve of the elastomer together with the data from a Mooney-Rivlin plot. The theory relating the ultimate properties to the viscoelastic properties of the elastomer is based upon the idea of a propagating crack, the rate of propagation being limited by viscoelastic mechanisms. Data for the failure curves and creep response for EPR and SBR elastomers are presented and shown to support the theory. Literature data for butyl rubber are also shown to confirm the theory.
Dynamic Testing of Automotive Rubber Parts by the Resonant Beam Tester. Effect of Polymer, Deflection, Age, and Temperature on Dynamic Rate
Authors: Lowman M. , Keller H. E.
Published: February 2011

When the recipe is basically the same, different polymers differ in dynamic rate and damping. Ethylene—propylene terpolymer, SBR, neoprene, and butyl gave higher dynamic rate and higher damping than natural rubber, polyisoprene, and the blend of polyisoprene and cis 1,4-polybutadiene. The lowest dynamic rate and lowest damping is obtained with polyisoprene. At room temperature, polymers having the highest damping also have the largest ratio of dynamic to static rate. One cannot predict the effect of temperature on dynamic rate by measuring static rate at these temperatures. Increase in temperature lowers dynamic rate, decrease in temperature increases it. This effect was least with a blend of polyisoprene and cis 1,4-polybutadiene, closely followed by polyisoprene, and natural rubber. The largest change was with butyl. Dynamic rate increases with time after cure. After 26 hr, dynamic rate is a function of the logarithm of time. This effect is least with polyisoprene. Natural rubber, SBR, EPT, neoprene and a blend of polyisoprene with cis 1,4-polybutadiene all follow Equation (1). Butyl has, by far, the greatest change in dynamic rate with time. Reducing the deflection from 0.012 in. to 0.004 in. linearly increased the dynamic rate. Times of vibration between 2 minutes and 60 minutes at room temperature had no effect on dynamic rate.
Friction on Wet Surfaces of Tire-Tread-Type Vulcanizates
Authors: Sabey Barbara E. , Lupton G. N.
Published: February 2011

A laboratory investigation has been made into the variation with temperature of the hardness and resilience of a wide variety of rubber compounds of the tire tread type. The effect of hardness and resilience on the fractional properties of the compounds under wet conditions has also been studied. In the first series of tests the resilience and hardness of 25 compounds were measured over a temperature range 0° to 80° C. All were vulcanized tire tread type compounds, and the basic materials used comprised 14 natural rubbers, 7 styrene/butadiene (SBR) rubbers, 2 butyl, 1 polybutadiene, and 1 ethylene/propylene. The tests showed a marked increase in resilience with increasing temperature for all compounds except the polybutadiene; the hardness of all compounds changed very little with temperature, only a slight decrease being observed over the whole temperature rise. Nine compounds of representative resilience and hardness were selected for a second series of tests in which friction was measured over a temperature range 1° to 40° C on seven surfaces representing roads of different textures. For eight of the compounds, friction values decreased with increase in temperature; for the other compound the friction increased to a maximum value at 30° C. These changes in friction cannot be explained by changes in hardness of the compounds, but they are in accordance with resilience changes, taking into account the different test conditions obtaining in the friction and resilience tests. The friction tests also showed that with the portable skid-resistance tester used to measure friction the sharpness of the projections in the road surface is more important than their size in determining the friction values under wet conditions, even when rubber compounds of low resilience are used. The implications of the findings and their application to the study of friction between tire and road are discussed. In particular, they have a bearing on the correct interpretation of resilience measurements of tire tread materials in relation to friction values under wet conditions.
Polymer—Solvent Interaction Parameter and Creep of Ethylene—Propylene Rubber
Authors: Dudek T. J. , Bueche F.
Published: February 2011

The polymer—solvent interaction parameter for an ethylene—propylene ter-polymer containing 53 mole-% ethylene was determined as a function of degree of crosslinking in n-heptane and benzene. A well characterized EPR gum vulcanizate was used to obtain the polymer-solvent interaction parameter in fourteen solvents, and the cohesive energy density of the terpolymer was evaluated. The composite tensile creep curves for gum and filled EPR vulcanizates were obtained and compared with SBR creep curves.