Butyl rubber vulcanization

Scagliusi, R.S., Cardoso, E.C.L., Lugao, A.B. Radiation-induced degradation of butyl rubber vulcanized by three different crosslinking systems. Radiat. Phys. Chem. 81, 991-994 (2012)... 

Unfilled butyl rubber, vulcanized or unvulcanized, degrades very quickly when exposed to sunlight and air. Addition of carbon black absorbs UV light so that no degradation takes place near the surface [697]. 

In the linear viscoelasticity regime, the principle of time-temperature superposition that was developed for polymer melts seems to work equally well for unfilled elastomers. Data of /(co), / ( )), and values of tan 5 = / (co)//(cl)) versus co for butyl rubber vulcanized with sulfur to various extents over a wide range of temperature (from -25°C to 50°C) were shown separately to collapse on master curves with a temperature shift factor a-j- obeying the general form of the WLF equation. Figure 9.23 shows the results for tan 5 [42]. Each curve represents the master curve for data of a giveu... 

Butyl mbber, a copolymer of isobutjiene with 0.5—2.5% isoprene to make vulcanization possible, is the most important commercial polymer made by cationic polymerization (see Elastomers, synthetic-butyl rubber). The polymerization is initiated by water in conjunction with AlCl and carried out at low temperature (—90 to —100° C) to prevent chain transfer that limits the molecular weight (1). Another important commercial appHcation of cationic polymerization is the manufacture of polybutenes, low molecular weight copolymers of isobutylene and a smaller amount of other butenes (1) used in adhesives, sealants, lubricants, viscosity improvers, etc. 

Butyl Rubber. Butyl mbber was the first low unsaturation elastomer, and was developed ia the United States before World War II by the Standard Oil Co. (now Exxon Chemical). It is a copolymer of isobutylene and isoprene, with just enough of the latter to provide cross-linking sites for sulfur vulcanization. Its molecular stmcture is depicted ia Table 1. 

Sulfur chemistry [29] has also been used to crosslink rubber/resin PSAs, although the use of elemental sulfur itself yields tapes that can stain substrates. Other patents exemplify the use of typical rubber vulcanizing chemistry such as Tetrone A , dipentamethylenethiuramtetrasulfide, and Tuads , tetramethylthiu-ram disulfide [30], or zinc butyl xanthate [31] for this purpose. Early art [32] also claimed electron beam curing of both natural rubber and other adhesives that were solvent coated on tape backings. Later references to electron beam curing... 

It is possible to distinguish between SBR and butyl rubber (BR), NR and isoprene rubber (IR) in a vulcan-izate by enthalpy determination. In plastic-elastomer blends, the existence of high Tg and low Tg components eases the problems of experimental differentiation by different types of thermal methods. For a compatible blend, even though the component polymers have different Tg values, sometimes a single Tg is observed, which may be verified with the help of the following equation ... 

The accelerated sulfur vulcanization of general-purpose diene rubbers (e.g., NR, styrene-butadiene rubber [SBR], and butadiene rubber [BR]) by sulfur in the presence of organic accelerators and other rubbers, which are vulcanized by closely related technology (e.g., ethylene-propylene-diene monomer [EPDM] mbber, butyl rubber [HR], halobutyl mbber [XIIR], nitrile rubber [NBR]) comprises more than 90% of all vulcanizations. 

Fig. 105.—Tensile strengths of butyl rubber fractions each vulcanized to the same cross-linking density p, corresponding to Me = 37,000, plotted against the primary molecular weight M. ...

Fig. 106.—Tensile strengths of the vulcanized butyl rubber fractions (Fig. 105) plotted against (M This quantity is propor-...

The materials selected for evaluation included three materials currently being used in these applications Biomer (Thoratec Laboratories Corporation, Emeryville, CA), representative of segmented ether-type polyurethanes Avcothane-51 (Avco Everett Research Laboratory, Inc., Everett, MA), a block copolymer of 10% silicone rubber and 90% polyurethane and Hexsyn (Goodyear Tire and Rubber Company, Akron, OH), a sulfur vulcanized hydrocarbon rubber that is essentially a polyhexene. Also selected, because of their easy availability, were Pellethane (Upjohn Company, North Haven, CT), an ether-type of polyurethane capable of being extruded in sheet form, and a butyl rubber formulation, compounded and molded at the National Bureau of Standards. The material thickness varied, but the sheets were generally about 1 mm thick. 

An estimation of ZnCFO efficiency as vulcanization active component was carried out in modelling unfilled elastomeric compositions on the basis of isoprene, butadiene-nitrile, chloroprene and butyl rubbers of sulphur, thiuram, peroxide, metaloxide and resin vulcanization systems. 

Figure 9. Vulcanization kinetics of modeling unfilled elastomeric compositions on the basis of butyl rubber of resin vulcanization at 160°C with ZnO or ZnCFO...

ZnCFO is the effective vulcanization active component of the sulfur, thiuram, peroxide and metaloxide vulcanization systems for isoprene, nitrile-butadiene and chloroprene rubbers at the same time it is not effective in resin vulcanization system for butyl rubber. On a degree of positive influence on the properties of elastomeric compositions vulcanization systems with ZnCFO are arranged in a line ... 

PP/EPDM-V Vulcanized EPDM dispersed in polypropylene PP/NBR-V Vulcanized nitrile rubber dispersed in polypropylene PP/IIR-V Vulcanized butyl rubber dispersed in polypropylene... 

PP/IIR-V, a dynamically vulcanized butyl rubber dispersed in a polypropylene... 

Butyl rubber, polyisobutylene, is an example of cationic polymerization with an acid. Review Chapter 14, Section 2.3. A small amount of isoprene is added to enable cross-linking during vulcanization through the allylic sites. 

The vulcanization of polychloroprene (Neoprene) is carried out in different ways. Vulcanization by sulfur, even with an accelerator, is not practiced to a large extent. Vulcanizations by metal oxides (without diamine), either alone or in combination with sulfur (sometimes together with an accelerator), give the best physical properties for the crosslinked product. Halogenated butyl rubber is crosslinked in a similar manner. The mechanism for crosslinking by metal oxide alone is not established [Stewart et al., 1985 Vukov, 1984]. 

Butyl rubber, containing only 0.5-2.5% isoprene units, is not efficiently crosslinked by sulfur. Chlorination of butyl rubber is carried out to improve its vulcanization efficiency by allowing a combination of sulfur and metal oxide vulcanizations. 

Butyl and Halobutyl Rubber. Butyl mbber is made by the polymerization of isobutylene a small amount of isoprene is added to provide sites for curing. It is designated HR because of these monomers. Halogenation of butyl mbber with bromine or chlorine increases the reaction rate for vulcanization and laminates or blends of halobutyl are feasible for production of mbber goods. It is estimated that of the 100 million kg of butyl (HR) and halobutyl (HIIR) mbber in North America, over 90% is used in tire applications. The halogenated polymer is used in the innerliner of tubeless tires. Butyl mbber is used to make innertubes and curing bladders. The two major suppliers of butyl and halobutyl polymers in North America are Exxon and Bayer (see ELASTOLffiRS, synthetic-butyl rubber). 

Polymers with solubility parameters differing from those of the solvent by at least 2.0 H, will not dissolve in the solvent at room temperature. Thus although unvulcanized natural rubber (NR), unvulcanized styrene-butadiene elastomer (SBR), unvulcanized butyl rubber, and EPDM dissolve in gasoline or benzene, the vulcanized (cross-linked) polymers are swollen but will not dissolve due to the presence of the crosslinks. 

Butyl rubber is produced by a process in which isobutylene is copolymerized with a small amount of isoprene using aluminum chloride catalyst at temperatures around — 150° F. (20). The isoprene is used to provide some unsaturation, yielding a product that can be vulcanized (43). Vulcanized Butyl rubber is characterized by high tensile strength and excellent flex resistance furthermore, as a result of its low residual unsaturation (only 1 to 2% of that of natural rubber) it has outstanding resistance to oxidative aging and low air permeability. These properties combine to make it an ideal material for automobile inner tubes (3), and Butyl rubber has continued to be preferred over natural rubber for this application, even when the latter has been available in adequate supply. 

Butyl rubber is one product formed when isobutylene is copolymerized with a few percents of isoprene. In the Exxon process an isobutylene-methyl chloride mixture containing a small amount of isoprene is mixed at — 100°C with a solution of AICI3 in methyl chloride. An almost instantaneous reaction yields the product, which is insoluble in methyl chloride and forms a fine slurry. Molecular weight can be controlled by adding diisobutylene as a chain-transfer agent. Increased catalyst concentration and temperature also result in lowering molecular weight. The product can be vulcanized and is superior to natural rubber. A solution process carried out in C5-C7 hydrocarbons was developed in the former Soviet Union.471,472... 

Polymers account for about 3—4% of the total butylene consumption and about 30% of nonfuels use. Homopolymerization of butylene isomers is relatively unimportant commercially. Only stereoregular poly(l-butene) [9003-29-6] and a small volume of polyisobutylene [25038-49-7] are produced in this manner. High molecular weight polyisobutylenes have found limited use because they cannot be vulcanized. To overcome this deficiency a butyl mbber copolymer of isobutylene with isoprene has been developed. Low molecular weight viscous liquid polymers of isobutylene are not manufactured because of the high price of purified isobutylene. Copolymerization from relatively inexpensive refinery butane—butylene fractions containing all the butylene isomers yields a range of viscous polymers that satisfy most commercial needs (see OLEFIN POLYMERS ELASTOMERS, SYNTHETIC-BUTYL rubber). 

Table 10. Effect of promoter8 on the properties of vulcanized butyl rubber M ...

Un-vulcanized butyl rubber/PVC lining for autoclave vulcanization or hot-air vulcanization. 

Pre-vulcanized Butyl Rubber/PVC Lining with Cold Bond Adhesive System... 

Un-vulcanized Butyl Rubber/PVC Lining for Autoclave Vulcanization or Hot-air Vulcanization... 

Known as EPR. this material is of limited use hecausc it cannot be vulcanized in readily available systems. However, (he rubbers arc made from low -cost monomers, have good mechanical and elastic properties, and outstanding resistance to ozone, heal, and chemical attack. They remain flexible to very low temperatures (brittle point about -95 C), They are superior to butyl rubber in dynamic resilience. 

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