Cold Vulcanization Research Articles

Organotin Compounds in Industrial Catalysis. I. (Re)esterification Processes

This is the first part of a series of reviews on the application of organotin compounds as the catalysts for some important industrial processes, such as (re)esterification and production of polyurethanes, and also as the catalysts for cold vulcanization of silicones and other practically important processes. The first review considers the application of organotin compounds in (re)esterification processes.

Dynamic mechanical properties of elastomeric nanoparticle composites

The blends of two crosslinked polystyrene-b-polyisoprene (PS-b-PI) copolymers with homopolystyrene were investigated for their dynamic mechanical properties. Elastomeric block copolymer nanofibers utilized as filler were prepared by employing the phase separation property of a polystyrene-b-polyisoprene copolymer, which was then exposed to a crosslinking agent (S2Cl2) for cold vulcanization. The crosslinking density and morphology of nanofillers resulted in three elastomeric block copolymer nanofillers: fully cross-linked nanofiber (FCF), fully crosslinked multi-junctioned nanofiber (FCM), and partially crosslinked multi-junctioned sample (PCM). Uncrosslinked PS-PI block copolymer (UBC) was also studied as a comparison. Crosslinking density was calculated by measuring the change in intensity of the double bond peaks using FTIR spectroscopy. Thermo-mechanical properties and morphology of the blends were characterized by dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). DMA results show that modulus increases with increasing filler loading in the terminal region for both PS/FCM and PS/FCF systems and the increasing rate is related to crosslinking density. Open image in new window

A study of an elastomeric coating based on EPDM of cold vulcanization

Studies of the thermostability of vulcanizates of ethylene–propylene–diene rubbers (EPDM) obtained by using dinitrosogenerating systems of low-temperature vulcanization are performed. It is shown that vulcanizates retain sufficient high properties in operation up to 200°C for a long time. The use of such compositions for producing thin rubber coatings applied on a number of insulating materials allows the effect of energy saving to be obtained.

Effect of Elastomeric Nanoparticles on Polystyrene/Organic Nanocomposites

The rheological behavior of nanosheet composites and the effect of morphology between elastomeric nanofiber and nanosheet composites were studied using a Cross-Williamson model and critical volume concentration was investigated by percolation threshold theory for fiber and sheet morphologies. Nanofiber and nanosheet particles were synthesized by a cold vulcanization process using a S2Cl2cross-linking reagent resulting from self-assembly of a PS-PI block copolymer. Nanofiber and nanosheet characterization was done by SEM. Rheological properties were measured and analyzed in terms of varying nanofiller and nanosheet loading from 0.5 to 10 wt%. For the nanofiber and nanosheet composites, the moduli were increased with increasing filler loading, whereas moduli of SI23 and SI43 composite decreased with increasing content. Both nanofiber and nanosheet composites showed a nanosized filler effect and their structural changes were between 5 and 10 wt%. Cross-Williamson three-parameter model was used to find zero-shear viscosity and relaxation time. Percolation threshold theory was used to study structural changes and calculate values.

Copolymers of vinylidene fluoride, hexafluoropropylene, and perfluoroallyl fluorosulfate

Radical copolymerization of vinylidene fluoride (1,1-difluoroethylene), hexafluoropropylene (hexa-fluoropropene-1), and perfluoroallyl fluorosulfate (fluorocopolymer C26-FS) was performed in a solution of 1,1,2-trifluoro-2,2,1-trichloroethane in order to create new low-molecular functional fluorocopolymers for cold vulcanization. The optimal copolymerization conditions were determined and a relationship was revealed between the microstructure of the C26-FS fluorocopolymer and its physicomechanical characteristics. 19F NMR spectroscopy was used to identify the structure and determine the number-average molecular mass and composition of the synthesized fluorocopolymers with a fluorosulfate group. The thermal stability in an inert medium and the glass transition temperature of S26-SF and the physicomechanical properties of their vulcanizates were studied. It was shown the properties and vulcanization duration of low-molecular functional fluorocopolymers is affected by the content of perfluoroallyl sulfate units (f = 2–4) relative to the vinylidene fluoride and hexafluoropropylene units in the polymer chain.

Vulcanized Ethene-PMO: A New Strategy to Create Ultrastable Support Materials and Adsorbents

A periodic mesoporous organosilica (PMO) functionalized with sulfur units between the organic bridges has been successfully synthesized by a postsynthetic cold vulcanization treatment performed on an ethenylene-bridged PMO material (ethene-PMO). The results of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption/desorption porosimetry show that the resultant materials have well-ordered hexagonal mesoporous structures with narrow pore size distributions. Moreover, 13C CP/MAS NMR, 29Si MAS NMR, X-ray photoelectron spectroscopy (XPS), and elemental analysis prove the cross-linking between the organic moieties through additional sulfur bridges. Besides the incorporation of a new functionality to this PMO, the vulcanization treatment, reminiscent of that applied to rubber, improves the thermal and hydrothermal stabilities of the material. The vulcanized materials were employed as mercury adsorbents able to be reused without loss of their capacity in repetitive adsorpt...

Single-component silicon sealing materials

Single-component silicon adhesive sealant of cold vulcanization based on liquid polyorganosiloxane resins with terminal hydroxyl groups designed at the State Research Institute of Chemistry and Technology of Organoelement Compounds are presented. It was demonstrated that due to their high performance characteristics, in particular the wide range of working temperatures (from −90 to +300°C), these materials draw interest from both civilian and special fields of industry. Methods of producing single-component silicon adhesive sealants were considered.

Multicompartment Core Micelles of Triblock Terpolymers in Organic Media

The formation of multicompartment micelles featuring a “spheres on sphere” core morphology in acetone as a selective solvent is presented. The polymers investigated are ABC triblock terpolymers, polybutadiene-b-poly(2-vinyl pyridine)-b-poly(tert-butyl methacrylate) (BVT), which were synthesized via living sequential anionic polymerization in THF. Two polymers with different block lengths of the methacrylate moiety were studied with respect to the formation of multicompartmental aggregates. The micelles were analyzed by static and dynamic light scattering as well as by transmission electron microscopy. Cross-linking of the polybutadiene compartment could be accomplished via two different methods, “cold vulcanization” and with photopolymerization after the addition of a multifunctional acrylate. In both cases, the multicompartmental character of the micellar core is fully preserved, and the micelles could be transformed into core-stabilized nanoparticles. The successful cross-linking of the polybutadiene core is indicated by 1H NMR and by the transfer of the aggregates into nonselective solvents such as THF or dioxane.

Controlled crosslinking of polybutadiene containing block terpolymer bulk structures: A facile way towards complex and functional nanostructures

The controlled crosslinking of polystyrene-block-polybutadiene-block-poly(tert-butyl methacrylate) (SBT) block terpolymers in their microphase-segregated bulk state is investigated. Two different methods, cold vulcanization and free radical crosslinking as well as its optimized procedure, the thiol–polyene method, are applied for crosslinking the lamellar polybutadiene microdomains within the lamella–lamella (ll) morphology of SBT bulk structures. It was found that the microphase-separated structures of the block terpolymers react very sensitively towards the addition of swelling solvents and crosslinking agents. The changes in the microphase-segregated morphologies are followed at all stages with transmission electron microscopy to give an in-depth view of the nanoscopic transformations. These partially unexpected changes in the morphologies make a careful adjustment and optimization of the reaction conditions necessary. For cold vulcanization, i.e. the reaction of double bonds with sulphur monochloride, several swelling solvents and concentrations of crosslinking agents are explored. In the case of free radical crosslinking, it is found that an increase of the radical initiator concentration above 5wt% does not lead to an increase of insoluble material as radical chain cleavages occur as side reactions, thus limiting the amount of the desired gel fraction. However, the addition of a trifunctional thiol can further increase the desired network formation. By means of this procedure and a subsequent homogenization, it is possible to create novel disc-like Janus particles. Dynamic light scattering and scanning force microscopy are used to highlight the flat nanoparticle structure and to demonstrate the influence of the crosslinker on the formed structures.

Fabrication of Crosslinked Block Copolymer Nanoparticles Using Cold Vulcanization

ABSTRACTThe aim of this study is to understand the crosslinked system of poly(styrene)-bpoly(isoprene) copolymer using cold vulcanization process as a facile method to produce anisometric nanoparticles. The morphologies of block copolymers could be controlled by the type of monomers, block junction, composition, and block size. A systematic methodology, utilizing cylindrical and lamellar morphologies of PS-b-PI copolymer, was used for producing fiber and sheet shaped nanoparticles. The cold vulcanization process was accomplished using sulfur monochloride (S2Cl2) as crosslinking agent. The microstructures and crosslinking density of crosslinked PS-b-PI copolymers were imaged and characterized. This study demonstrated the crosslinking of microphase separated block copolymer as a method to create particles with controlled size, shape, and physical properties.

Rapid method of determination of the molecular weight distribution of polyethylene terephthalate

Method of determination of molecular weight distribution of PETP 1959 this process depends on many factors: concentration of low molecular weight thiokol and base, extent of load on the sample, temperature, sulphur content in the polymer and conditions of vulcanization. The results of these investigations will be discussed later. The authors are grateful to V. A. Byl'ev for his part in the discussions. CONCLUSIONS (1) A device is proposed for continuous registration of polymer swelling by an electric potentiometer. (2) A study of swelling ofthiokol vulcanizates shows that, as well as the main network, salt bonds participate in forming the vulcanization structure on cold vulcanization, and in filled vulcanizates, bonds formed by reaction of the polymer with carbon black are readily decomposed during swelling. It was shown that swollen vulcanizates can undergo flow and degradation with low molecular weight thiokol in the presence of a base, diphenylguanidine.

Gamma-ray vulcanization of rubber

An experimental study was made of the vulcanization of rubber by the cross-linking action of intense gamma radiation from a Co 60 source. Vulcanization by heat and chemicals is an important, highly developed industrial process, the essential feature of which is the chemical cross linking of the rubber molecules by sulphur atoms. With gamma-ray vulcanization, the cross-linking occurs by the elimination of hydrogen and the formation of carbon-carbon bonds, which are more stable than sulphur bonds. The usual vulcanizing agents and sulphur werefound to have only slight influence on gamma-ray vulcanization, but fillers enhanced the effects of the radiation, probably through scattering or other interaction with the photons. The tensile strengths developed with a series of fillers were found to increase with the specific volumes of the fillers. Tensile strengths obtained with gamma-ray vulcanization were not as high as can be secured by conventional vulcanization. The radiation dose required for vulcanization was relatively large, 1 to 5 × 10 7 rep. If there were no heat losses, such a dose would raise the temperature of the rubber to ordinary vulcanizing temperatures. Typical potential advantages of gamma-ray vulcanization include uniform vulcanization of thick articles, more stable, better ageing vulcanizates, cold vulcanization of extruded shapes or preforms, and faster preliminary processing of the rubber stock. The development of industrial applications of gamma-ray vulcanization may be contingent on the economical utilization of fission-waste products or spent reactor-fuel elements and developments in the technology of working with intense radiations.

Vulcanization of Crepe Rubber by Sulfur Monochloride. II. The Dilatometric Method

Abstract The vulcanization of rubber by sulfur monochloride is believed to consist of the cross-linking of adjacent isoprene units by thio-ether bonds. Such a reaction, involving polymer aggregation, should be accompanied by an increase of the density of the rubber, and, by choosing a suitably delicate technique, it should be possible to measure the rate of vulcanization by observing density changes. A dilatometric method seemed most suitable, and it was found that the reaction could indeed be followed by observing the rate of decrease of volume of the system rubber-sulfur monochloride when dissolved in a suitable solvent. Initial experiments showed that, during cold vulcanization, the system underwent a volume contraction which was of the order of 10 per cent with respect to the rubber. This comparatively large contraction allowed one to work with extremely dilute solutions (<0.3% w/w) of rubber. It thereby became possible to study the systems under more ideal kinetic conditions of high dilution than has been hitherto possible. In the present investigation, it has not been possible to do more than establish the broad outlines of the kinetic behavior of the system, and, on this basis, to propose feasible mechanisms for the cold vulcanization process.

Vulcanization of Crepe Rubber by Sulfur Monochloride. I. The Gelation Method

Abstract When a dispersion of rubber (4 per cent) in benzene is treated with sulfur monochloride (1 per cent) at room temperature, the solution becomes opaque and gelation occurs in a few minutes. With a more dilute dispersion of rubber (1 per cent), Meyer and Mark obtained a weak gel, which could be broken up by stirring to give, after one hour, a pale yellow precipitate, corresponding to the formula C10H16SCl2. By analogy with the reaction of ethylene and sulfur monochloride, these workers proposed the following reaction process: (see PDF for diagram) The so-called cold-vulcanization process, which is essentially the above reaction, thus appears to correspond to the cross-linking of adjacent isoprene units by means of thioether-bond formation. This result contrasts with the hot sulfur vulcanization process, where the reaction does not involve the sulfurization of any appreciable number of olefinic groups. The mechanism of the cold vulcanization process is unknown. However, it is known that certain commercial sulfur vulcanization accelerators speed up the above gelation process to a remarkable extent. The present work describes an attempt to investigate the kinetics of the reaction between rubber and sulfur monochloride, with the eventual view of establishing the mechanism of the process. In general, two main methods have been developed for assessing reaction velocities. They are the dilatometric method and a more arbitrary time-of-gelation method. While the former method is of importance in studying the more detailed quantitative features of the reaction, the latter method is of help as a powerful auxiliary. Although it is not yet possible to propose a clear-cut mechanism for the vulcanization process, certain kinetic features have been established, and indications of the most fruitful lines of attack are presented.

Dilatometric Measurement of the Rate of Vulcanization of Crepe Rubber by Sulfur Monochloride

Abstract The cold vulcanization of rubber by sulfur monochloride is believed to consist essentially of the cross-linking of adjacent polyisoprene units by a series of sulfide bonds. Chemical analysis of the product suggests that the cross-linking process is analogous to the mustard gas reaction of ethylene with sulfur monochloride, thus: (see PDF for diagram) Nothing is known, however, about the kinetics of this vulcanization process. General considerations lead one to expect that such a reaction, involving polymer aggregation, should be accompanied by an increase in the density of the rubber; moreover, by choosing a suitably delicate technique, it should be possible to utilize such density changes for rate determinations. A dilatometric method seemed most suitable, and the experiments described here show that the vulcanization process is, indeed, accompanied by a decrease in volume of the reaction mixture, and that the reaction may be followed quantitatively using a tap dilatometer.

Partially Chlorinated Derivatives of Rubber

Abstract Chlorinated rubbers containing from 1 to 17 per cent of chlorine were prepared by direct chlorination, at ordinary temperature, of crepe rubber dissolved in carbon tetrachloride. These products retain, to a greater or lesser degree, rubberlike properties, and are capable of hot or cold vulcanization with or without the addition of vulcanizing agents. The resulting vulcanizates are considerably more resistant to the swelling action of solvents, and also to the action of chlorine, than corresponding products prepared from crepe rubber. The resistance to swelling agents increased with increase in combined chlorine content; tensile strength and elasticity, however, decreased with increasing chlorine content. As expected, hardness increased with increase of chlorine content, and vulcanizates from derivatives containing more than 10 per cent combined chlorine were not sufficiently rubberlike to warrant many experiments. Fully chlorinated rubber was compatible with partially chlorinated rubber, and addition of the former was necessary for vulcanizates to pass the Post Office flame test for cables.

Partially chlorinated derivatives of rubber

AbstractChlorinated rubbers containing from 1 to 17% of chlorine have been prepared by direct chlorination, at ordinary temperature, of crèpe rubber dissolved in carbon tetrachloride. It has been found that these products retain, to a greater or lesser degree, rubber‐like properties and are capable of hot or cold vulcanization with or without the addition of vulcanizing agents. The resulting vulcanizates have been shown to be considerably more resistant to the swelling action of solvents, and also to the action of chlorine, than corresponding products prepared from crèpe rubber. The resistance to swelling agents increased with increase of combined chlorine content; tensile strength and elasticity, however, decreased with increasing chlorine content. As expected, hardness increased with increase of chlorine content and vulcanizates from derivatives containing more than 10% combined chlorine were not sufficiently rubber‐like to warrant many experiments. It was found that fully Chlorinated rubber was compatible with partially chlorinated rubber and addition of the former was necessary for vulcanizates to pass the Post Office flame test for cables.

Estimation of the Stability of Rubber Solutions

Abstract Various types of rubber products, such as seamless goods and rubberized fabrics, are prepared from rubber solutions and are vulcanized either by the hot or cold process. “Cold vulcanization” is effected either by sulfur chloride vapor or by very dilute solutions of sulfur chloride in solvents such as carbon disulfide, carbon tetrachloride, or benzine. “Hot vulcanization” is carried out by heating with sulfur, organic accelerators, and inorganic substances such as colloidal zinc oxide, to “activate” the accelerators. To safeguard against any unforeseen difficulties, it is necessary not only to ascertain how much tendency mixtures containing powerful accelerators have to vulcanize, but above all to determine for how long a time a solution remains stable, i. e., does not commence to vulcanize during ordinary use. To obtain an insight into the practical utility of a mixture, it is in general necessary merely to heat the mixture at 110° C. in a press. A mixture can be regarded without hesitation as satisfactory for practical use if it shows no indication of vulcanization after one hour at this temperature. On the other hand, products prepared from such a solution should as a rule vulcanize fully in 30 mm. at 125° C. or perhaps in 40–50 mm. at 110° C. In view of this, the practical utility of a mixture is judged by the tendency for incipient vulcanization to take place when the mixture is heated at 70° C. in a press. In the case of solutions of rubber mixtures which contain all ingredients milled into the rubber before the solution is prepared, incipient vulcanization is evident by gelation of the solution, i. e., a change from sol to gel. With mixtures of this kind, incipient vulcanization at 70° C. in a press may be accepted as a reasonable criterion, but in no case should it be regarded as a trustworthy indication of the stability of a solution up to the point of gelation, for the rate of vulcanization of the solution to the point of gel formation, and during gel formation itself, is influenced considerably by the constitution and the concentration of the solvent. The concentration of the solution and the degree of plasticity of the rubber mixture likewise influence gel formation. A test of the dry mixture at 70° C. in a press for incipient vulcanization does not take account of these factors.

Contribution to the Study of the Vulcanization Reaction

Abstract In spite of the great technical importance of vulcanization, the chemical reaction involved is not yet entirely understood, although at the present time it is assumed that chemical phenomena take part in this operation. To C. O. Weber in particular is due much of the research in the field of rubber. It was he who proved the chemical combination with sulfur. He assumed that during hot vulcanization, sulfur combines with two polyprene chains and that they unite chemically, but he was not able to go into this subject in more detail or to prove anything further. The process of cold vulcanization is better understood. There are good reasons for assuming that sulfur chloride reacts with the double bond of polyprene chains in the same way that it does with olefins of low molecular weight, for example with ethylene. It is known that sulfur chloride unites with this latter according to the following scheme:

A Simplification and Improvement in the Determination of Copper in Fabrics and Rubberized Materials

Abstract The determination of small quantities of copper in fabrics and in rubberized materials can be simplified by destruction with concentrated nitric acid, which accelerates the ignition to the final ash. At the same time, this method avoids the usual danger of volatilization of copper as chloride as a result of the presence of chlorine from white factice or from cold vulcanization. Likewise, precipitation of the copper as sulfide can be avoided by repeating the precipitation of the extract from the ash, which contains predominantly aluminum and iron, with ammonia. In this second precipitation, only around 1 to 2 per cent of the total quantity of copper is retained in the precipitate and filter, and this quantity may in most cases be neglected. The ordinary colorimetric method used in the past for the detection of copper as complex cuprammonium ion can be made about ten times as sensitive by making use of the reaction: Cu+ + + 2I− → CuI + I. This is, however, applicable only in the complete absence of the ferric ion and of nitric acid in the test solution. The sensitivity can be increased still more by the addition of starch. Another advantage of the determination of copper by measurement of the equivalent quantity of iodine lies in the fact that, if necessary, only one-tenth as much sample need be used, but in this case as in all such determinations, the copper must be distributed uniformly throughout the material to be analyzed.