# Multifunctional Modifying Systems Based on Ionic Liquids for Epoxy Resin Systems and Composites
## 1 Introduction
However, the most important ability of ionic liquids with respect to different types of fibers is their ability to initiate and stimulate the fibrillation process of the fiber [35; 36]. This phenomenon involves the splitting of the main structure of the fiber with the simultaneous formation of a network of microfibers that diverge from the main stem. During fibrillation, the fibers additionally undergo twisting by which a layer of microfibers is formed around the shaft. So far, the effect of ionic liquids in initiating fiber fibrillation has been successfully confirmed for both: natural [37] (silk, cellulose) and synthetic (aramid) fibers [38]. Recent studies show the potential of ionic liquids to impart fire-resistant material characteristics to composites. For this purpose, work is carried out with the use of PhILs, from which it is known to use, for example, ethyltributylphophonium diethyl phosphate [39], 1-vinyl-3-(diethoxphosphoryl)-propylimidazolium bromide [40] or imidazolium diphenylphosphionate [41], which can act as both a flame-retardant and an epoxy resin hardener. Sometimes, to increase these properties, admixtures of graphene suspended in an ionic liquid are used [16]. Research on flame retardants in recent years has focused on the search for new compounds with effective action and has largely consisted of organic synthesis of substances based on previously known flame retardants (structural improvements of substances, new derivatives) or synthesis of completely new molecules. The mechanism of flame retardancy is, in general, a set of physicochemical reactions and processes that can occur in the gaseous (flame) or condensed (plastic, decomposition products) phase [12; 18]. Predicting and designing the mechanisms of flame retardancy is a difficult task [42], and studies show that even compounds containing the same amount of phosphorus, with very similar spatial structures, can flame retard the material in different ways. This is due to dependencies in the molecule such as (i) susceptibility to esterification reactions (hydroxyl groups, acid groups) or (ii) the ability of the flame retardant to migrate inside the resin network [18]. Typically, a flame retardant can simultaneously act in both the gaseous and condensed phases but maintain a preference for one or the other. The mechanism of flame retardancy focuses on the following effects: (i) reducing heat release during combustion, (ii) reducing the amount of smoke and gas released during combustion, and (iii) restricting oxygen, not sustaining combustion [43; 44]. However, research on flame retardants has centered around the use of additive-type flame retardants, such as cyclophosphamide derivatives [7], DOPO (9,10-dihydro-9-oxa-10-phosphphenanthrene-10-oxide), or ammonium polyphosphates and resorcinol bis(diphenyl diphosphate) [15]. Although the synergistic effect between ionic liquids and inert compounds has been studied [13; 14; 16], it has not been considered in the context of using as flame retardants only ionic compounds such as ionic liquids, which, containing phosphorus, silicon, and nitrogen atoms, may also exhibit a synergistic effect. The examples cited illustrate the extensive impact of ionic liquids on resin systems and composites, highlighting the multitude of factors that must be carefully considered to accurately evaluate their cumulative effects on specific materials. At the same time, the cited examples inspire and justify the study of ionic liquids in the context of the search for multifunctional compounds that can perform a function in the area of composite materials on many levels. The aim of the study was to explore the possibility of creating a multifunctional system that modifies both the properties of the epoxy resin and the composite itself on multiple levels. The key task was to identify the areas of influence of the modifications and to assess the intensity of their impact.