Ionic Liquid (1-Ethyl-3-methylimidazolium Acetate) Plasticization of Chitosan-Based Bionanocomposites

The structure and properties of different biopolymer composites based on chitosan and chitosan/carboxymethyl cellulose (CMC) are governed by multiple structure-property relationships associated with different phase interactions. Plasticization of these matrices with ionic liquid 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) played a dominant role, increasing the mobility of biopolymer chains as well as ions and associated dipoles but reducing biopolymer chain interactions, crystallinity, and thermal stability. These structural changes led to higher matrix ionic conductivity, shorter electrical relaxation time, and greater matrix ductility. The inclusion of graphene oxide (GO) and reduced GO (rGO) also influenced the structure and properties of these bionanocomposites by disrupting the biopolymer hydrogen bonding and/or polyelectrolyte complexation (PEC) and interacting with [C₂mim][OAc]. The impact of GO/rGO was more evident for 20 wt % [C₂mim][OAc], such as increased crystallinity and thermal stability of chitosan. PEC was hindered with excess (40 wt %) [C₂mim][OAc] added and further hindered again when rGO was included. This study shows that the structure and properties of bionanocomposites are not just determined by the surface chemistry of GO/rGO but can also be influenced by multiple interactions involving plasticizers such as ILs and additional biopolymers.