Chlorobutyl elastomer

Capps, R.N. Beumel, L.L. "Influence of Fillers on Constrained-Layer Vibration-Damping Capabilities of Chlorobutyl Elastomers", J. Acoust. Soc. Am. 83, S82(A), 1988. 

Fig. 32 Kinetic characteristics for thermal oxidation of some rubbers assessed at three temperatures. The data were taken from [96J1]. (white) butyl elastomer, (dark grey) chlorobutyl elastomers, (pale grey) bromobutyl elastomer, (a) induction time of oxidation, (b) oxidation rate, (c) maximum oxidation time.

Exxon Mobil in brochures argues that butyl elastomer (HR) apparently is miscible with chlorobutyl elastomer (CIIR) and bromobutyl elastomer (BUR). This occurs because they have the same backbone structure of polyisobutylene and polyisoprene with an occasional different functional group of chlorine and bromine, respectively [33,34]. 

Chlorobutyl rubber is prepared by chlorination of butyl rubber (chlorine content is about 1 wt%). This is a substitution reaction produced at the allylic position, so little carbon-carbon double unsaturation is lost. Therefore, chlorobutyl rubber has enhanced reactivity of the carbon-carbon double bonds and supplies additional reactive sites for cross-linking. Furthermore, enhanced adhesion is obtained to polar substrates and it can be blended with other, more unsaturated elastomers. 

FIGURE 9.18 (continued) (b) Resilience measurements of elastomers. Samples of chlorobutyl rubber (CIIR), polybutadiene rubber (BR), and cross-linked recombinant resilin. (From Elvin, C.M., Carr, A.G., Huson, M.G., Maxwell, J.M., Pearson, R.D., Vuocolol, T., Liyou, N.E., Wong, D.C.C., Merritt, D.J., and Dixon, N.E., Nature, 437, 999, 2005.)... 

Butyl rubber is not compatible with natural rubber, SBR, nitrile rubber or with any other elastomer having an appreciable degree of unsaturation modified butyls (chlorobutyl and bromobutyl) are compatible with such elastomers and used as liners in tubeless tyres to improve air retention. 

The elastomer determines most of the physical and chemical characteristics of a rubber compound. Typical elastomers are natural elastomers such as natural rubber (NR), sometimes called crepe, and synthetic elastomers such as butyl (including chlorobutyl and bromobutyl), ethylene propylene diene monomer (EPDM), and styrene butadiene rubber (SBR). A list of commonly used elastomers is shown in Table 2. 

The choice of elastomer has the greatest effect on a formulation. The most common elastomers that can be used for closures for injectable products are given in Table 12.5. Of these elastomers, natural rubber, synthetic polyisoprene, butyl, chlorobutyl and bromobutyl rubber are typically used for the manufacture of rubber closures and stoppers used in the packaging and administration of parenterals. 

Novel process on the base of compact tubular reactors is principally fitted for production of bromobutyl rubber and also others chlorinated elastomers. Process is accepted at OAO "Nizhne-kamskneftekhim". In 2001-2002 pilot plant worked at which chlorobutyl rubber of required quality was received without any problems. Technical schedule was made. At present experimental-industrial plant is projected. 

Figure 3 Resilience measurements of cross-linked elastomers chlorobutyl rubber (CNR), polybutadiene rubber (BR), and cross-linked recl-resilin. Reproduced with permission from Elvin, C. M. Carr, A. G. Huson, M. G. etal. Nature 2005,437,999. Copyrighf 2005 Nature Publishing Group.

Use of a chemically saturated rubber such as chlorobutyl, together with styrene as the monomer, with the rubber the predominant component by weight, results in a material similar in behavior to the thermoplastic elastomers (see Chapter 4). In all cases two glass transitions and other evidence suggested phase separation. 

Uses Accelerator for polychloroprene elastomers, halobutyl rubbers esp. chlorobutyl used for mech. goods, cables, hoses, membranes, fabric proofings, vulcanizing sol ns. 

Accelerated-sulfur vulcanization is the most widely used method. For many applications, it is the only rapid crossUnking technique that can, in a practical manner, give the delayed action required for processing, shaping, and forming before the formation of the intractable vulcanized network. It is used to vulcanize natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), butyl rubber (HR), chlorobutyl rubber (ClIR), bromobutyl rubber (BUR), and ethylene-propylene-diene-monomer rubber (EPDM). The reactive moiety for all of these elastomers can be represented by... 

The first two fractions are produced either in a nitrogen atmosphere or under vacuum at 70 Pa (0.5mmHg). Accurate quantification requires appropriate corrections to allow for the overlap of the process oil and resins with the polymer decomposition region along with the serious complication observed for elastomers with a heteroatom in the monomer unit like acrylonitrile-butadiene, chloro-prene rubber, chlorobutyl rubber, polyvinyl chloride (PVC), chlorosulfonated polyethylene, polyacrylates, fluoroelastomers, epichlorohydrin rubbei etc. Most of these polymers produce volatile components below 300°C and leave a carbonaceous residue after degradation, which oxidizes with the carbon black... 

In bromobutyl/chlorobutyl rubber blends, both elastomers have the polyisobutylene backbone and halogen reactive functionality. These polymers, being molecularly miscible, constitute an ideal system for co-vulcanization. Bromobutyl and chloro-butyl can be used interchangeably without significant effect on state of cure as measured by extension modulus, tensile strength, and cure rheometer torque development. Bromobutyl will increase the cure rate of a blend with chlorobutyl. However, where bromobutyl is the major part of the blends, chlorobutyl does not reduce scorch tendencies because the more reactive halogen unit can dominate. 

When producing the hromo- and chlorobutyl rubbers, the halogen basic elastomer is used. Like the nmi-halogen basic elastomer, this contains relatively few unsaturated bonds. 

Fig. 24.1 Structural formulas of (a) basic elastraner in latex (b) basic elastomer of butyl rubber, in which x = chlorobutyl rubber x = Br for bnnnobutyl rubber (c) basic elastomer of silicone rubber...

Halogenation of the isoprene enchainments in butyl elastomers yields halobutyl elastomers. Reaction of the isoprene units with elementary bromine or chlorine leads to the formation of allylic halide units along the chain—a substitution as opposed to addition across the double bonds. This leads to much faster curing, which permitted the development of tubeless tires, as adhesion of halobutyl to the rest of the tire could be achieved. Halobutyls are primarily used by the tire industry to form the inner liner of the tubeless tire. Other applications are similar to that of butyl. Chlorobutyl is also used in pharmaceutical stoppers. 

Walters and Keyte [102] first observed dispersed particles in blends of rubber pol)m[iers by phase contrast optical microscopy. Marsh et al [103] studied elastomer blends by both optical phase contrast and TEM. Electron microscopy was applied to study blends of natural rubber, st)n-ene-butadiene rubber (SBR), a s-polybuta-diene (PB) and chlorobutyl rubber [104]. It became obvious that both hardening of the... 

Special check valves are available for sewage and slurry flows. The Red Valve Company Series 39 valves (Figures 2-19 and 2-20) feature a special reinforced elastomer check sleeve. The valve check sleeve seals under reverse flow or back-pressure and opens under pressure from the pump. It does not incorporate any discs that may wear on contact with slurry. This type of valve is therefore different in design than the type shown in books on water flows. The consultant engineer should therefore request from the manufacturer of the slurry check valves the estimated K factor for pressure losses. The Red Valve Company Series 39 slurry check valves are available in sizes up to 48" (1220 mm), with a choice of elastomers such as pure gum rubber, neoprene, Hypalon, chlorobutyl, Buna-N, EPDM, and Viton. 

Exxon butyl rubber and its chlorinated analog, chlorobutyl rubber are isobutylene-isoprene copolymers. They are basically inert, nonpolar, stable elastomers which exhibit outstanding resistance to attack by a great many different chemicals. 

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... 

Bromobutyl rubber is a little more expensive to produce than chlorobutyl rubber however, it will sometimes give better adhesion than chlorobutyl rubber to other elastomer-based compounds. Also, bromobutyl rubber cures a little faster than chlorobutyl. However, bromobutyl rubber may also have a greater tendency than chlorobutyl rubber to impart scorch problems to a compound during processing. 

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