SPECIALTY POLYMERS AND DYNAMICALLY VULCANIZED ALLOYS FOR ULTRA LOW AIR PERMEABILITY TIRE INNER LINERS

Abstract

ABSTRACT Brominated poly(isobutylene-co-p-methylstyrene) specialty elastomers (Exxpro™) or BIMSM (ASTM name) are unique in their low permeability to air combined with a low glass transition temperature, Tg,, and a saturated backbone; making them a choice elastomer for applications requiring air barrier properties. This behavior derives from the geminal dimethyl groups on every other carbon of the polyisobutylene (PIB) backbone causing modification in the bond angles of these chains, allowing them to pack more closely than other saturated hydrocarbons. Dynamically vulcanized alloys (DVAs), also known as thermoplastic vulcanizates (ASTM 5046) of Exxpro™ elastomer and nylon thermoplastic (Exxcore™ DVA), also referred to as BIMSM-Nylon DVA, have much lower permeability to air than BIMSM. The challenge is to maintain the elastomeric nature of the material by having a major volume fraction of BIMSM rubber, while approaching the excellent air barrier characteristics of nylon at a lower volume fraction of the thermoplastic matrix than the dispersed rubber phase. This problem was solved by introducing a functional oligomer that chemically reacts with the nylon. BIMSM-Nylon DVAs consist of submicron sized domains of BIMSM elastomer of tailored molecular structure, in a matrix of nylon and a chemically bound oligomer viscosity modifier. Thus, a reasonable elastomeric modulus is achieved, and the key performance properties of superior air barrier as well as low temperature fatigue resistance are well satisfied. Tire inner liners are the focused end use of BIMSM-Nylon DVA, where the novel material characteristics are targeted to achieve excellent air impermeability, durability, and lightweighting. Optimal combination of these properties is expected to deliver improved performance and sustainable benefits such as fuel economy and lower tire maintenance costs.