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

Pei Chen,Tony Mcnally,Fengwei Xie,Fengzai Tang

doi:10.1021/acsomega.0c02418

Abstract

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.

Highlights

Biopolymers, which are defined as macromolecules formed by living organisms according to the IUPAC, have attracted much interest in materials development in recent years due to their renewability, biodegradability, and inherent functionality
carboxymethyl cellulose (CMC) matrix plasticized by 20 wt % [C2mim][OAc] without nanofiller) exhibited a clear morphology without particulate features seen for the A-samples
There are several interactions among different components in chitosan and chitosan/CMC polyelectrolyte complexed bionanocomposites, as summarized below: (1) graphene oxide (GO) and reduced GO (rGO) were effectively dispersed in both matrices by thermomechanical mixing

Summary

■ INTRODUCTION

Biopolymers, which are defined as macromolecules (including proteins, nucleic acids, and polysaccharides) formed by living organisms according to the IUPAC, have attracted much interest in materials development in recent years due to their renewability, biodegradability, and inherent functionality (e.g., antimicrobial activity of chitosan). With a higher [C2mim][OAc] content, AE4-F displayed an even lower Td value (259 °C), further testifying the effect the IL has in reducing the biopolymer thermal stability. The combined effects of inclusion of GO or rGO and a high [C2mim][OAc] content resulted in a lower degree of PEC and hydrogen bonding between chitosan and CMC so that the decomposition peak for CMC became more pronounced. Compared with AE4-F, AE4/rGO showed the M′′ peak at a slightly lower f, whereas for AE4/GO-F, M′′ kept increasing up to the highest f tested This could be linked to the effect of the nanofiller on the availability of free, mobile ions, and dipoles in the samples, as already proved in the discussion on σdc. The addition of rGO was not effective, whereas GO notably increased θc60s, which, again, can be ascribed to the interaction between GO and the IL

■ CONCLUSIONS

M formic acid rGO solution

■ ACKNOWLEDGMENTS