Ionic liquid-functionalized reinforcements in epoxy-based composites: A systematic review

Several high-performance reinforcements may be used in epoxy-based composites. These commonly undergo chemical and/or physical treatments to enhance their interfacial interactions with polymer matrices. One recent technology comprises the use of ionic liquids (IL) as compatibilizers. This strategy may result in the development of composite materials with greater performance or multifunctional characteristics. Herein, an overview in the area of IL-modified reinforcements and their effect on epoxy-based composites is presented. The PRISMA protocol was followed for the review, and the focus of these studies was on the modification of carbon nanotubes, followed by graphene/graphite nanoplatelets and bio-fillers. The most used IL were those based on imidazolium cation, especially 1-butyl-3-methylimidazolium chloride. In most cases, when IL are used, the reinforcement displays stronger interactions with the epoxy matrix, depending the treatment route employed. Improved interfacial interactions are cited as the main reason for the improvement in the composite mechanical and thermal performances. It was also found that strategies for using low IL content, or routes that enable recovery of the salts after fiber/particle treatment, are still required, as well as the study of the influence of different amounts/types of IL on the structure of fillers and their relationships with the composite properties.