Butyl rubber
Butyl rubber (abbreviation IIR), and isobutene- isoprene rubber (short: PIBI ), is a plastic selected from the group of elastomers and is one of the synthetic rubbers. It is a copolymer of 95-99 mole% of isobutene, and 1-5 mol% of isoprene.
Properties
Butyl rubber is often sold à 30 kg in yellowish- white homogeneous bales. It dampens vibration and shock energy well and provides good resistance to acids and bases. Furthermore, it has a very good weather and ozone resistance, high electrical insulation properties, a very low gas permeability and an elastic even at very low temperatures behavior. The disadvantage is its lack of resistance to oils and fats as well as its relatively low elasticity at room temperature. Of isoprene determines the number of double bonds, which are still present after the polymerization. These can be used for vulcanization or modification by halogens ( Chlorobutyl, bromobutyl). This different material parameters can be adjusted:
- Hardness 40-85 Shore A
- Tensile strength up to 20 N/mm2
- Elongation at break up to 700 %
- Operating temperature -40 ° C to 130 ° C
Butyl rubber (IIR ) may not (PIB) are mixed with the thermoplastic polyisobutylene.
Production
Butyl rubber was first synthesized in 1943 in Germany on a large scale. Since cationic polymerisation is a highly exothermic process, and to control the reaction rate, the preparation takes place at low temperatures ( -40 ° C to -100 ° C) in solution in hexane or by precipitation method with the solvent instead of methylene chloride; acid catalysts are aluminum (III ) chloride or boron trifluoride.
Application
Butyl rubber is used in inner tubes, tire inner liners, bladders, seals and diaphragms, rubber cable insulation, as chemical protective glove and as an ingredient in chewing gum. Also for the sealing of insulating glass as well as in adhesives and various heterogeneous solid rocket fuels butyl rubber is used.
Halo-butyl rubber
Butyl rubber can be improved in its characteristics by halogenation. For this, the rubber is dissolved in an inert solvent and with vigorous stirring chlorine gas or liquid bromine is added. The resulting hydrogen halides are neutralized with sodium hydroxide.