Full definition
Butyl rubber, also known as IIR (Isobutylene-Isoprene Rubber), is a synthetic rubber that is primarily composed of isobutylene and a small percentage of isoprene. This unique copolymer structure gives butyl rubber its remarkable properties, making it one of the most effective materials for applications requiring low gas permeability. In fact, butyl rubber exhibits gas permeability that is 8-10 times lower than that of natural rubber (NR), which is a significant advantage in applications such as tire innerliners. The material can effectively maintain air pressure, which is crucial for the performance and safety of tires. Additionally, butyl rubber features excellent vibration damping characteristics, with a rebound resilience of only 12-20%, the lowest among commercial rubbers. This property is particularly beneficial in applications where shock absorption is necessary, such as vibration isolation mounts.
The temperature performance range of butyl rubber is impressive, typically spanning from -45°C to +120°C for standard grades, and can go up to +150°C for halobutyl grades (chlorobutyl and bromobutyl variants). This thermal stability allows butyl rubber to maintain its performance in a variety of environmental conditions. Key properties include outstanding resistance to ozone and weathering, which is due to its nearly saturated polymer backbone. Furthermore, it demonstrates excellent chemical resistance to dilute acids, alkalis, and polar solvents, making it suitable for use in chemical tank linings and pharmaceutical applications. However, butyl rubber does have limitations; it has poor resistance to hydrocarbon solvents and mineral oils, and its very low unsaturation complicates co-vulcanization with other rubber types.
Halobutyl variants, such as chlorobutyl (CIIR) and bromobutyl (BIIR), were developed to address the co-cure challenges associated with standard butyl rubber. These halogenated versions are essential components in tubeless tire innerliners, enhancing their air retention capabilities while allowing for compatibility with other materials. The global production of butyl rubber is approximately 1.3 million tonnes per year, with leading manufacturers including ExxonMobil, Lanxess, and PJSC Nizhnekamskneftekhim. The ASTM D2000 classification for butyl rubber is AA, indicating its high-quality standards and suitability for various industrial applications.