Butyl Vulcanisates

Butyl vulcanisates swell considerably in oleic acid and lose their physical properties. Silica fillers however give better resistance in 20% formic acid. 

In oxalic acid a slight swelling (5%) occurs for butyl vulcanisates and as such physical properties are not very much affected. Acetic acid on the other hand attacks the black... 

Unsaturated polymers undergo reactions such as isomerisation, cyclisation, addition, epoxidation and hydrogenation. Saturated polymeric hydrocarbons undergo substitution on the main chain or the side chain. Loaded butyl vulcanisates were shown to be less... 

In the presence of light, halogens attack both vulcanised and unvulcanised butyl rubber. Whether vulcanised or unvulcanised the effect of the reaction is to produce rapid deterioration in molecular weight. A strip of butyl vulcanisate suspended in bromine gas degrades rapidly. In a few minutes the specimen becomes fluid enough to drip to the bottom of the vessel. Chlorosulfonated polyethylene is resistant to ozone being better than Neoprene and butyl rubber compounds [18]. 

Antioxidants and antiozonants are not needed in properly compounded butyl vulcanisates for most applications. However, for applications requiring optimum resistance to weather and ozone (e.g. electrical... 

Halobutyl rubbers cannot be compounded to give the extraordinary level of moisture resistance that may be achieved with butyl vulcanisates because some of their vulcanisation by-products are water-soluble salts. For this reason they are not used in high-voltage electrical insulation but they possess sufficient moisture resistance to give outstanding performance in hose tubes and covers for hot water and superheated steam. 

Halobutyl vulcanisates usually contain small quantities of electrolytes. Consequently, they are less moisture resistant than butyl vulcanisates and are less suitable for use in electrical insulation. Nevertheless, as their structure restricts the thermal motion needed for diffusion, and as the amount of electrolyte present is small, they absorb moisture very much less readily than many other hydrocarbon elastomers. Consequently, they are capable of providing excellent service in such applications as hose tubes for hot water and superheated steam, and tank linings for aqueous solutions of corrosive chemicals. 

Styrene—butadiene, acrylonitrile—butadiene, and butyl latices have also been prevulcanised, but this usually results in a lower wet gel strength. Where the mbber is to be deposited onto a fabric substrate, as in manufacture of fabric-lined gloves, the lower gel strength is not a problem. For unsupported dipped synthetic mbber products, however, the use of post-vulcanised compounds is more common. 

Resin Cure. Resin cure systems yield carbon—carbon cross-links and, consequendy, thermally stable materials. Butyl mbber vulcanised with resins are used as tire-curing bladders, and have a life of 300—700 curing cycles at steam temperature of 175°C at about 20 m/cycle. 

Mechanical properties depend considerably on the stmctural characteristics of the EPM/EPDM and the type and amount of fillers in the compound. A wide range of hardnesses can be obtained with EPM/EPDM vulcanisates. The elastic properties are by far superior to those of many other synthetic mbber vulcanizates, particularly of butyl mbber, but they do not reach the level obtained with NR or SBR vulcanizates. The resistance to compression set is surprisingly good, in particular for EPDM with a high ENB content. 

Whilst polyisobutene is a non-rubbery polymer exhibiting high cold flow (see Section 11.3), the copolymer containing about 2% isoprene can be vulcanised with a powerful accelerated sulphur system to give moderately rubbery polymers. The copolymers were first developed in 1940 by Esso and are known as butyl rubbers and designated as HR. As they are almost saturated they have many properties broadly similar to the EPDM terpolymers. They do, however, have two properties that should be particularly noted ... 

Vulcanisation can be effected by diamines, polyamines and lead compounds such as lead oxides and basic lead phosphite. The homopolymer vulcanisate is similar to butyl rubber in such characteristics as low air permeability, low resilience, excellent ozone resistance, good heat resistance and good weathering resistance. In addition the polyepichlorohydrins have good flame resistance. The copolymers have more resilience and lower brittle points but air impermeability and oil resistance are not so good. The inclusion of allyl glycidyl ether in the polymerisation recipe produces a sulphur-curable elastomer primarily of interest because of its better resistance to sour gas than conventional epichlorhydrin rubbers. 

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

In an acetone extract from a neoprene/SBR hose compound, Lattimer et al. [92] distinguished dioctylph-thalate (m/z 390), di(r-octyl)diphenylamine (m/z 393), 1,3,5-tris(3,5-di-f-butyl-4-hydroxybenzyl)-isocyanurate m/z 783), hydrocarbon oil and a paraffin wax (numerous molecular ions in the m/z range of 200-500) by means of FD-MS. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out (Chapter 2). The method of Dinsmore and Smith [257], or a modification thereof, is normally used. Mass spectrometry (and other analytical techniques) is then used to characterise the various rubber fractions. The mass-spectral identification of numerous antioxidants (hindered phenols and aromatic amines, e.g. phenyl-/ -naphthyl-amine, 6-dodecyl-2,2,4-trimethyl-l,2-dihydroquinoline, butylated bisphenol-A, HPPD, poly-TMDQ, di-(t-octyl)diphenylamine) in rubber extracts by means of direct probe EI-MS with programmed heating, has been reported [252]. The main problem reported consisted of the numerous ions arising from hydrocarbon oil in the recipe. In older work, mass spectrometry has been used to qualitatively identify volatile AOs in sheet samples of SBR and rubber-type vulcanisates after extraction of the polymer with acetone [51,246]. 

Chlorinated butyl rubber. Chlorination or bromination of butyl rubber overcomes the difficulty of vulcanising butyl rubber in mixtures with more highly unsaturated substances due to the preferential absorption of the sulphur by the more highly unsaturated component. Chlorohydrin Rubbers... 

Also known as vulcanite and (mainly in the USA) hard rubber . The hard, horn-like product obtained when natural rubber and some synthetic rubbers such as nitrile (NBR) are vulcanised with a high proportion of sulphur or organic nonsulphur vulcanising agent. Butyl rubber and polysulphide rubber do not form ebonites. Ebullioscopy... 

A non-sulphur vulcanising agent of particular application in butyl rubber compounds, the activator being red lead. 

Polymerised isobutylene, a non-vulcanisable, rubber-like polymer. See Butyl Rubber. Polyisoprene... 

Quinone and some of its derivatives may be used in the non-sulphur vulcanisation of natural rubber. The best-known derivative is para-quinone dioxime used as a curing agent for butyl rubbers. 

Vulcanisation of elastomers effected by the incorporation in the compound of certain polymeric resins derived from the condensation of formaldehyde with 4-alkyl phenols. Most frequently used with butyl and EPDM compounds for enhanced heat resistance. 

Elemental sulphur mixed into mbber compounds is the agent responsible for the vulcanisation of the majority of mbber products made from natural mbber, SBR, butyl mbber and nitrile mbber. Sulphur-vulcanisable varieties of many of the newer synthetics are also available. The bulk... 

The most important limitation of polyisobutene is its tendency to cold flow because of which it cannot be used in self-supporting forms. This defect can be overcome by copolymerisation with isoprene and vulcanisation of product with sulphur. The product is called butyl rubber. This product was first marketed in 1943 in USA. 

Vulcanised butyl rubber is very similar to vulcanised natural rubber in various physical characteristics but has better resistance to oxidation and has low permeability to gases. Hence, it is widely used in tubes for cycles, scooters, motor cars, etc. It is also used as rubber in many other applications. 

Poly-isobutylene (PIB) is a very useful rubber because of its very low gas permeability. Co-polymerised with small amounts of isoprene (to enable vulcanisation with sulphur) to butyl rubber (HR), it is the ideal rubber for inner tubes. If PIB would crystallise, it could not be used as a technical rubber The same holds for the rubbers BR and IR. 

Butyl rubber (IIR) is derived from polyisobutylene, a polymer which is not further mentioned in this chapter, which has a rubbery nature, but which can not be vulcanised in the conventional way with sulphur. This objection is taken away by copolymerisation with a small amount of isoprene. Butyl rubber has a very low resilience, but outrivals all other rubbers in resistance to gas permeation for that reason it is generally used for tyre inner tubes. 

Adhesives on the basis of a rubber are applied as watery dispersions, as solvents, or as solvent-free fluids. Sometimes the rubber is vulcanised after the gluing process, sometimes it remains uncured. Polymers often used are butyl rubber, polyisobutylene, and polychloroprene. A more recent development is the use of... 

The chemical microstructures of cis-polyisoprene (HR) vulcanised with sulfur and N-t-butyl-2-benzothiazole sulfenamide (TBBS) accelerator were studied as a function of extent of cure and accelerator to sulfur ratio in the formulations by solid-state 13C NMR spectroscopy at 75.5 MHz [29]. Conventional (TBBS/Sulfur=0.75/2.38), semi-efficient (SEV=1.50/1.50) and efficient (EV=3.00/1.08) vulcanisation formulations were prepared, which were cured to different cure states according to the magnitude of increase in rheometer torque. The order and types of the sulfurisation products formed are constant in all the formulation systems with different accelerator to sulfur ratios. However, the amount of sulfurisation has been found to vary directly with the concentration of elemental sulfur. 

Similar vulcanisation chemistry is observed with the N- -butyl-2-benzothiazole sulfenimide (TBSI) accelerated sulfur-vulcanisation of HR [26] compared to the TBBS accelerated systems... 

Vinyl or vinylidene chloride/acrylonitrile copolymers Chlorosulphonated polyethylene, vulcanised chloroprene, chlorinated butyl rubber... 

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