Rubber mixtures

Insoluble Sulfur. In natural mbber compounds, insoluble sulfur is used for adhesion to brass-coated wire, a necessary component in steel-belted radial tires. The adhesion of mbber to the brass-plated steel cord during vulcanization improves with high sulfur levels ( 3.5%). Ordinary rhombic sulfur blooms at this dose level. Crystals of sulfur on the surface to be bonded destroy building tack and lead to premature failure of the tire. Rubber mixtures containing insoluble sulfur must be kept cool (<100°C) or the amorphous polymeric form converts to rhombic crystals. 

Figure 9.7 Comparison of experimental and calculated vapour pressures of benzene in benzene-rubber mixtures [7],...

In the area of environmental protection the Japanese tyre firm Toyo is doing more as a tyre producer than the law demands. In this article Wilhelm Hoeppner, responsible for publicity at Toyo Reifen GmbH, explains in an interview how Toyo is involved. It looks at rubber mixtures, the problem of nitrosamines, legal environmental stipulations, economic impact and the future efforts by Toyo. 

Schoenmakers et al. [72] analyzed two representative commercial rubbers by gas chromatography-mass spectrometry (GC-MS) and detected more than 100 different compounds. The rubbers, mixtures of isobutylene and isoprene, were analyzed after being cryogenically grinded and submitted to two different extraction procedures a Sohxlet extraction with a series of solvents and a static-headspace extraction, which entailed placing the sample in a 20-mL sealed vial in an oven at 110°C for 5,20, or 50 min. Although these are not the conditions to which pharmaceutical products are submitted, the results may give an idea of which compounds could be expected from these materials. Residual monomers, isobutylene in the dimeric or tetrameric form, and compounds derived from the scission of the polymeric chain were found in the extracts. Table 32 presents an overview of the nature of the compounds identified in the headspace and Soxhlet extracts of the polymers. While the liquid-phase extraction was able to extract less volatile compounds, the headspace technique was able to show the presence of compounds with low molecular mass... 

Application Tests. Physicochemical and special analytical test methods allow the classification of carbon blacks and a rough estimation of their application properties. Exact data on the application properties of a carbon black in a special system, e.g., plastic material or a rubber mixture, can only be given by application tests under nearly practical conditions. 

Mooney viscosity—measure of the resistance of raw or unvulcanized rubber to deformation, as measured in a Mooney viscometer. A steel disc is embedded in a heated rubber specimen and slowly rotated. The resistance to the shearing action of the disc is measured and expressed as a Mooney viscosity value. Viscosity increases with continued rotation, and the time required to produce a specified rise in Mooney viscosity is known as the Mooney scorch value, which is an indication of the tendency of a rubber mixture to cure, or vulcanize, prematurely during processing. 

Separate work on a Fourier transform (FT) NMR spectrometer revealed the presence of two peaks from the solvents from both within and outside the swollen gel [104], See below for a discussion of the origin of the NMR linewidths. The chemical shift of the olefinic peaks was found to shift down field with increasing crosslink density, and hence a modified method for determining H% was introduced. In this paper they also introduced the first 13C NMR measurements of swollen rubber blends, and again found a systematic increase in linewidth with increasing crosslink density. The higher resolution in the 13C spectrum compared with NMR allows the potential of more detailed information on rubber mixtures. 

Methylphenyldimethoxysilane is used as a stabiliser (antistructuring additive) in the production of rubber compounds based on silicone elastomers and highly active fillers. Introducing up to 10% (weight) of methylphenyldimethoxysilane into a rubber mixture improves the physicochemical properties of vulcanised rubbers and helps to preserve the technological characteristics of the compounds in storage. 

According to a JSR patent Nd-catalysis allows for the polymerization of BD in the presence of carbon black. By this method a BR/carbon black master batch is obtained. The master batch technology eliminates time and energy consuming mixing of carbon black and rubber [340,341]. According to this patent the content of bound rubber (amount of rubber which can be extracted from a carbon black/rubber mixture with an appropriate solvent, e.g. toluene) is increased and vulcanizate properties are improved. 

Some dicyanate-containing compositions, which contain rubbers as flexibilizing components, were described in the preceding chapters. There were also patent applications made, where dicyanates were claimed as additives in typical rubber mixtures. In such mixtures, butadiene-acrylonitrile rubber is used. The main components of such binders are nitrile rubber, BPA/DC and methylethylketone. They contain, moreover, Zn octoate and Fe203 [144] or ZnO and sulfur [145]. Isoprene-acryloni-trile rubber, BPA/DC prepolymer, Zn octoate, DABCO and benzoyl peroxide were dissolved in a methylethylketone-dimethylformamide mixture. Glass fiber was impregnated with the obtained solution [146]. 

A rubber mixture contains ethylene-propylene rubber, BPA/DC, CaC03, ZnO, sulfur, dicumyl peroxide and mineral oil. The final product has elevated thermal stability [147]. 

Nitrile Rubbers. Mixtures of butadiene, acrylonitrile, and DBPF were polymerized in bottles at 35°C. using the following recipe ... 

When only spectroscopic methods are used, they are able to identify polymer components with respect to their chemical nature. However, in many cases, they are unable to answer the question whether two chemical structures are combined to yield a copolymer or a blend or both. For example, analyzing a rubber mixture one is able to identify styrene and butadiene as the monomer units. However, using FTIR or NMR it is impossible to decide if the sample is a mixture of polystyrene (PS) and polybutadiene (PB),or a copolymer of styrene and butadiene, or a blend of a styrene-butadiene copolymer and PB. For the latter case, even the copolymer composition cannot be determined just by running a FTIR or NMR spectrum. 

A-Nitrosamines in rubber products are by-products of the reactions taking place during the vulcanization of rubber mixtures [80]. They are formed from some chemical compounds such as secondary amines (accelerators, antioxidants) via nitrosation by nitrogen oxides present in the surrounding air. These reactions occur inside the rubber product and on its surface. The resulting A-nitrosamines from the interior of the rubber can diffuse to the surface of the article, and then to the environment or media in which the product is used. A-Nitrosamines can also be incorporated in the rubber mixture by contamination of raw materials during preparation. 

In 1954, Dow finally perfected a can process to make high-impact polystyrene (HIPS). The secret was that the traditional can process could not simply be used since the product would be full of gel particles of rubber ( fish-eyes ) instead, the styrene-rubber mixture was first carried out to 30% conversion with shearing agitation. Then the mixture was transferred to 10 gallon cans where the reaction was completed. This process was documented in the now famous Amos patent [18]. 

Several applications of analytical pyrolysis on natural rubber have been reported. One such application is the determination of particles of rubber in atmospheric dust [11]. In this work, isoprene peak was utilized for rubber identification in a Py-GC system, the pyrolysis being performed at 740° C. Most other applications were related to the determination of natural rubber in complex mixtures [3] and synthetic rubber mixtures. 

NN for the formulation of a rubber mixture. The net was used for the purpose of direct (what are the properties of the mixture when the composition is given) and indirect modeling (what should be the composition to ensure the required properties of the mixture). There have been adaptive usage of NN in learning how to map the relations between the inputs and outputs. 

Borosy, A. Quantitative composition-property modelling of rubber mixtures by utilising artificial neural networks. Chemomet. Intell. Lab. Syst. 1999, 47, 227-238. 

On the basis of the white soot BS-lOO with the ZnO jacket ( 20% in calculation for ZnO) a new activator of rubber mixtures vulcanization was made. On the one hand, it substitutes ZnO, on the other it has better characteristics in comparison with a mechanical mixture of the same composition [79]. 

The key point about assessing and defining process and product state similar to the machine operators way, is having objective information about the product quality. In the presented approach, the information from the optical inspection system was used to define characteristic situations based on the profile quality (the kind, distribution and quantity of defects) and the process parameters measured and stored by the automation system. A situation or case is thus characterized, among other things, by the aforementioned profile quality, the kind of profile that is produced, the used rubber-mixture, environmental data like air pressure or humidity, the values and latest progression of physical process parameters hke extruder-temperature, power of microwave heating or speed of conveyor-belts and the countermeasures that are taken by the machine operators. 

Polymeric sulfur is produced commercially as insoluble sulfur (IS) and is used in the rubber industry [56] for the vulcanization of natural and synthetic rubbers since it avoids the blooming out of sulfur from the rubber mixture as is observed if Ss is used. The polymeric sulfur (trade-name Crys-tex [57]) is produced by quenching hot sulfur vapor in liquid carbon disulfide under pressure, followed by stabilization of the polymer (against spontaneous depolymerization), filtration, and drying in nitrogen gas. Common stabilizers [58] are certain olefins R2C=CH2 like a-methylstyrene which obviously react with the chain-ends (probably -SH) of the sulfur polymer and in this way hinder the formation of rings by a tail-bites-head reaction. In this industrial process the polymer forms from reactive small sulfur molecules present in sulfur vapor [59] which are unstable at ambient temperatures and react to a mixture of Ss and on quenching. 

VI. Rheological Behavior of Uncrossiinked Carbon Black-Rubber Mixtures 190... 

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