Ionic Conductivity and Structure of Chitosan Films Modified with Lactic Acid-Choline Chloride NADES.

Mikhail A Smirnov,Vitaly K Vorobiov,Alexander V Smirnov,Ivan V Abalov,Maria P Sokolova,Alexandra L Nikolaeva,Natalia V Bobrova

doi:10.3390/polym12020350

Mikhail A Smirnov, Vitaly K Vorobiov + Show 5 more

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https://doi.org/10.3390/polym12020350

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Abstract

The natural deep eutectic solvent (NADES) based on choline chloride (ChCl) and lactic acid (LA) was used for the preparation of chitosan (CS) films by the solution casting method. The content of NADES in films was from 0 to 82 wt%. The impact of NADES on the morphology and crystalline structure of films was investigated using scanning electron microscopy as well as wide-angle and small-angle X-ray scattering. The experimental results allow to propose CS chains swelling in NADES. FTIR spectroscopy confirms the interactions between CS and NADES components via the formation of hydrogen and ion bonds. The thermal properties of the composite films were studied by simultaneous thermogravimetric and differential thermal analysis. Thermomechanical analysis demonstrated appearance of two transitions at temperatures between −23 and −5 °C and 54–102 °C depending on NADES content. It was found that electrical conductivity of film with 82 wt% of NADES reaches 1.7 mS/cm. The influence of the composition and structure of films on the charge carriers concentration and their mobility is discussed.

Highlights

Chitosan (CS) is a linear copolymer composed of β-(1-4) linked 2-acetamido-2-deoxy-β-Dglucopyranose and 2-amino-2-deoxy-β-D-glycopyranose obtained by deacetylation of chitin
The ionically conducting films based on the chitosan and choline chloride, i.e., lactic acid natural deep eutectic solvent (NADES), were prepared with the NADES content up to 82 wt%. It was demonstrated by a combination of Fourier transform infrared (FTIR), scanning electron microscopy, wide-angle and small-angle
X-ray scattering, that components of NADES intensively interact with the polymer, that results in the “swelling” of polymer chains and decreasing of the degree of crystallinity

Summary

Introduction

Chitosan (CS) is a linear copolymer composed of β-(1-4) linked 2-acetamido-2-deoxy-β-Dglucopyranose and 2-amino-2-deoxy-β-D-glycopyranose obtained by deacetylation of chitin. The solid polymer electrolytes based on natural polymers have received significant attention during recent years [8] due to their environmental safety and low production cost Biopolymers such as CS and cellulose were used for preparation of ionically conducting membranes [9], separators for electrical double-layer capacitors [10,11], Li-ion batteries [12], thermopower generators [13] and supercapacitor electrodes [14]. It was reported that, due to high ion concentration, ILs are ideal electrolytes for accumulation of large charge carrier densities at low voltages This makes them promising for application in organic field-effect transistors based on polymer electrolytes [16]. Another prospective field for the application of ion Polymers 2020, 12, 350; doi:10.3390/polym12020350 www.mdpi.com/journal/polymers

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