Butyl rubbers curing system

Cure Systems of Butyl Rubber and EPDM. Nonhalogenated butyl rubber is a copolymer of isobutjiene with a small percentage of isoprene which provides cross-linking sites. Because the level of unsaturation is low relative to natural mbber or SBR, cure system design generally requites higher levels of fast accelerators such as the dithiocarbamates. Examples of typical butyl mbber cure systems, thein attributes, and principal appHcations have been reviewed (26). Use of conventional and semi-EV techniques can be used in butyl mbber as shown in Table 7 (21). 

Rodgers, B., Jacob, S., Curry, C., and Sharma, B.B. (2009) Butyl rubber curing bladder resin vulcanization systems compositions and optimization. Paper 107. Presented at a Meeting of the American Chemical Sodely Rubber Division, Pittsbmgh PA. 

Modified butyl rubbers—the crosslinked butyl and halogenated butyl rubbers—all possess the shock absorbency, stability and gas barrier properties that are characteristic of standard butyl rubbers. However, they differ from each other, and from standard butyl rubbers, in terms of the variables that distinguish standard butyl rubbers from each other, and in respects related to the types, amounts and functions of their modifiers. The crosslinked butyl rubbers resist flow, which is an important requirement in uncured sealant tape, their primary application. The halogenated butyl rubbers cure much faster than standard or crosslinked butyl rubbers, use less complicated curing systems and can be covulcanised with highly unsaturated elastomers. 

Table 7. Conventional and Semi-EV Cure Systems for Butyl Rubber ...

The low unsaturation requires powerful curing systems whilst the hydrocarbon nature of the polymer causes bonding problems. To overcome these problems chlorinated and brominated butyl rubbers (CIIR and BUR) have been introduced and have found use in the tyre industry. 

Curing systems. Four curing systems can be used for BR and chlorinated butyl rubber formulations. 

Butyl rubber(s), 4 433-458 9 561 14 265. See also Halogenated butyl rubber annual capacity, 4 451t carbon monoxide compatibility with, 5 4t chemical reactions, 4 448 copolymers, 4 444-446 cure systems for, 21 802-803 economic aspects, 4 451, 452t elastomeric vulcanizates, 4 448-450 formulation for reclaiming, 21 475t health and safety factors, 4 452-453 isobutylene polymerization mechanism, 4 434-436... 

Cure systems, for butyl rubber and EPDM, 21 802-803 Cure temperatures... 

The advanced applications for nitrocellulose plastisol propellants require that they be integrally bonded to the motor case. Successful case bonding for the multiyear storage life of a rocket calls for special adhesives and liners which are completely compatible with these highly plasticized propellants. Best results have been obtained with a combination of an impervious rubber liner and a crosslinked adhesive system with a limited affinity for the plasticizers used in the propellants. Examples of effective liners are silica-filled butyl rubber and chlorinated synthetic rubber. Epoxy polyamides, isocyanate-crosslinked cellulose esters, and combinations of crosslinked phenol-formaldehyde and polyvinyl formal varnishes have proved to be effective adhesives between propellant and impervious liners. Pressure curing of the propellants helps... 

In view of the wide application of Py—GC in industry and research, the development of techniques and equipment for automatic analysis by this method is of great practical interest. An automatic Py—GC system was developed by Coulter and Thompson [69] for Curie-type cells with a filament for specific application in the tyre industry. A typical analysis involves the identification and determination of polymers in a tyre material sample. The material of a tyre is essentially a mixture of polymers, most often natural rubber (polyisoprene), synthetic polyisoprene, polybutadiene and butadiene-styrene copolymer. A tube is normally made of a material based on butyl rubber and a copolymer of isobutylene with small amounts of isoprene. In addition to the above ingredients, the material contains another ten to twelve, such as sulphur, zinc oxide, carbon black, mineral oil, pine pitch, resins, antioxidants, accelerators and stearic acid. In analysing very small samples of the tyre material, the chemist must usually answer the following question on the basis of which polymers is the tyre made and what is their ratio The problem is not made easier by the fact that cured rubber is not soluble in any solvent. 

Commercially important elastomeric thermoplastic alloys are dynamically vulcanized blends of polypropylene with high volume fractions of EPDM, polybutadiene rubber, nitrile rubber, and butyl rubber (Santoprene , Vyram , Geolast and Trefsin ) all currently sold by Advanced Elastomer Systems, a joint venture of Monsanto and Exxon. Another recent member of the commercial dynamically cured elastomeric thermoplastic alloys is the blend of PVC and a crosslinked ethylene copolymer (Alcryn , DuPont). The current consumption of all the elastomeric thermoplastic alloys in the USA is over 23 kton/y, with the EPDM/PP blend (Santoprene ) assuming about 90% of the market share. 

Triforine cure accelerator Dipentaerythrityl acrylate cure activator, oxidation butyl rubber Benzothiazyl disulfide cure inhibitor, RTV systems Dimethicone, vinyidimethyl-terminated cure moderator, RTV systems Dimethicone, vinyidimethyl-terminated cure promoter, polyesters Benzene phosphinic acid cure promoter amine-cured epoxies Furfuryl alcohol curing agent... 

The low degree of unsaturation of butyl rubber, whilst having certain advantages, has the consequences of a low cure rate when using the conventional vulcanization systems used in diene rubbers. In turn this... 

Peroxide cross-linked terpolymers have a lower compression set than conventional butyl rubber vulcanizates and better ozone resistance than butyl rubbers of comparable unsaturation. Suitably stabilized, these systems have a heat resistance comparable to phenolic resin cured conventional butyl rubbers but with faster cure rates and higher compatibility with other types of rubber (Walker et ai, 1974). Some of these latter properties may also be shared with halogenated butyl rubber vulcanizates. 

The halogenated butyl rubbers may be cross-linked via either allylic hydrogen or the halogen group. As a broad generalization it may thus be considered that the materials may not only be cured by the methods used with butyl rubber but also those employed with polychloroprenes. The main systems to consider are ... 

The curing system developed for butyl rubbers has been extended to ethylene-propylene terpolymer (EPDM). Mechanisms of curing by p-dinitrosobenzene have been discussed. The cured cements are promising as outdoor sealants in terms of oxidative stability. 

Stearic acid is a usual processing aid in butyl rubber formulations, acting as lubricant and minimizing mill sticking apart from this action, it also plays the role of activator in the curing system. Hydrocarbon or phenolic tackifying resins are sometimes provided in compounds to assist the adhesion in confection or splicing. 

Based on the same virtually saturated PIB backbone, bromobutyl and chlorobutyl rubbers possess the same low permeability toward air, gases and moisture vapor of regular butyl rubbers. Their vulcanizates exhibit similar elastic features and higher vibration dampening in comparison with general-purpose (dienic) elastomers. The vulcanizates of CIIR and BUR obtained with many curing systems... 

FIG. 13 Comparison of the vulcanization behavior of butyl rubber (Exxon Butyl 268) with sulfur + accelerator and chlorobutyl rubber (Exxon Chlorobutyl 1066) with zinc oxide (----) at 149°C (-) at 166°C. Cure system for butyl rubber MBT, 0.5 phr TMTD, 1.0 phr sulfur, 2.0 phr. Cure system for chlorobutyl ZnO, 5.0 phr stearic acid, 2.0 phr. 

Poiyisobutylene rubber (IM) was a precursor to butyl rubber, which was first developed in Germany. However, this polymer had no unsaturation it could not be cured with a sulfur-based system. In 1937 Standard Oil (now ExxonMobil) developed the copolymer version that is used today in high volume. A small amount of isoprene provides the unsaturation that enables conventional curing with sulfur or other crosslinkers. 

Methanol is oxidized to formaldehyde to make RF resins (for RFL dips for cord adhesion to rubber), methylol-terminated PF resins (to cure butyl rubber), RF resins (for HRH rubber-to-metal adhesion system), HMMM (as a methylene donor in HRH rubber-to-metal adhesion system), IMP (to cure polyurethane elastomers), and 1,4-butanediol (to cure polyurethane elastomers). 

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