Thermoplastic Chitosan Plasticized with Deep Eutectic Solvent Derived from Gamma-valerolactone

Abstract

A new polyol derived from gamma-valerolactone with 10 carbon chain and four hydroxyl groups was used in combination with choline chloride for the production of a deep eutectic solvent (DES) employed as plasticizer for chitosan. The polyol estimated boiling point was 340 °C and the glass transition temperature (T_g) was − 6 °C. No crystallization temperature was observed due to the non-symmetric structure of polyol and because it is a mixture of stereoisomers. A eutectic condition was detected in an interval of choline chloride(ChCl)/polyol composition from 2:1 to 1:10. It was observed that only the mixtures with higher ChCl content showed melting points, so the eutectic composition was chosen by the lowest T_g that was obtained by the 1:1 molar ratio mixture, circa − 40 °C. This ChCl/Polyol composition was used to prepare plasticized chitosan film, by hot pressing. The glycerol/choline chloride mixture was also used as DES for comparison purposes. Both DES acted as plasticizer to obtain chitosan thermoplastic films, verified by the significant T_g drop from 165 °C, for unplasticized film, to -2 °C and − 30 °C, for films plasticized with DES based on ChCl-polyol and ChCl-glycerol, respectively. The materials plasticized with ChCl-polyol, showed a decrease in modulus of about 54% and an increase of 455% in elongation compared to ChCl/Glycerol, indicating better plasticization efficiency of the polyol based DES. The use of ChCl/Polyol have opened up a new opportunity for the use of chitosan as a plastic material and the high boiling point of polyol has made it a real and highly stable plasticizer.