Invented by Charles Goodyear, chemical cross-linking of rubbers by sulfur vulcanization is the only method by which modern automobile tires are manufactured. The formation of these cross-linked network structures leads to highly elastic properties, which substantially reduces the viscous properties of these materials. Here, we describe a simple approach to converting commercially available and widely used bromobutyl rubber (BIIR) into a highly elastic material with extraordinary self-healing properties without using conventional cross-linking or vulcanising agents. Transformation of the bromine functionalities of BIIR into ionic imidazolium bromide groups results in the formation of reversible ionic associates that exhibit physical cross-linking ability. The reversibility of the ionic association facilitates the healing processes by temperature- or stress-induced rearrangements, thereby enabling a fully cut sample to retain its original properties after application of the self-healing process. Other mechanical properties, such as the elastic modulus, tensile strength, ductility, and hysteresis loss, were found to be superior to those of conventionally sulfur-cured BIIR. This simple and easy approach to preparing a commercial rubber with self-healing properties offers unique development opportunities in the field of highly engineered materials, such as tires, for which safety, performance, and longer fatigue life are crucial factors.
In this study, the development and characterization of an intrinsically self‐healable material have been reported based on bromobutyl rubber (BIIR) modified with imidazole (Im) and loaded with carbon nanotubes (CNTs) as reinforcing and electrically conducting agent. The ionic imidazolium groups facilitate an ionic network, which imparts the composites a pronounced self‐healing behavior. The cation‐π bondings between modified BIIR and CNT surface improve the rubber‐filler interaction leading to a better mechanical performance and a higher electrical conductivity of the composites. It has been demonstrated that the healing process can be accelerated by applying an electrical current across a damaged surface of a test specimen owing to the Joule heating effect. The recovery of the mechanical and electrical properties of the composites is investigated under different test conditions and specifically discussed in terms of the rubber‐filler interactions and the filler dispersion. The applied scientific approach with the exploration of the unique nature of the imidazolium modified and CNT loaded BIIR may promote developments for a new class of rubber materials for different smart and technological applications.
Abstract:In this work, we report about the mechanical relaxation characteristics of an intrinsically self-healable imidazole modified commercial rubber. This kind of self-healing rubber was prepared by melt mixing of 1-butyl imidazole with bromo-butyl rubber (bromine modified isoprene-isobutylene copolymer, BIIR). By this melt mixing process, the reactive allylic bromine of bromo-butyl rubber was converted into imidazole bromide salt. The resulting development of an ionic character to the polymer backbone leads to an ionic association of the groups which ultimately results to the formation of a network structure of the rubber chains. The modified BIIR thus behaves like a robust crosslinked rubber and shows unusual self-healing properties. The non-covalent reversible network has been studied in detail with respect to stress relaxation experiments, scanning electron microscopic and X-ray scattering.
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