# Green Deep Eutectic Solvents for Functionalizing Chitosan–Dialdehyde Materials with Varied Crosslinker Content

## TL;DR

Researchers developed a new method to modify chitosan films using both dialdehyde starch and deep eutectic solvents, resulting in materials that are more flexible and have better surface properties for packaging.

## Contribution

This work introduces a dual-modification strategy combining covalent crosslinking and plasticization to enhance chitosan-based materials.

## Key findings

- Combining DAS and DES improves flexibility and reduces stiffness of chitosan films.
- DES increases surface roughness and hydrophilicity beyond roughness-driven effects.
- The dual-modification strategy significantly lowers Young’s modulus and increases elongation at break.

## Abstract

What are the main findings?
The combined use of DAS and DES enabled the generation of a balance between stiffness and flexibility.Incorporation of deep eutectic solvent into the DAS-crosslinked chitosan causes a substantial increase in surface roughness.DES markedly lowers the water contact angle, enhancing surface hydrophilicity beyond roughness-driven effects.

The combined use of DAS and DES enabled the generation of a balance between stiffness and flexibility.

Incorporation of deep eutectic solvent into the DAS-crosslinked chitosan causes a substantial increase in surface roughness.

DES markedly lowers the water contact angle, enhancing surface hydrophilicity beyond roughness-driven effects.

What are the implications of the main findings?
DES plasticization enables more flexible Ch/DAS films and easier processing.An optimized DAS amount in Ch/DES films ensures a balanced compromise between stiffness, strength, and flexibility.Lower water CA implies higher polarity at the interface, aiding food coating creation.

DES plasticization enables more flexible Ch/DAS films and easier processing.

An optimized DAS amount in Ch/DES films ensures a balanced compromise between stiffness, strength, and flexibility.

Lower water CA implies higher polarity at the interface, aiding food coating creation.

A series of chitosan-based films was obtained by combining the covalent crosslinking of chitosan with dialdehyde starch (DAS) and plasticization using a choline chloride–malonic acid deep eutectic solvent (DES), thereby engineering their structural, mechanical, and surface properties for advanced packaging applications. DAS was synthesized via periodate oxidation of potato starch and characterized by FTIR and quantification of aldehyde groups through acid–base titration, enabling precise control of the –NH2 (chitosan) to –CHO (DAS) molar ratios (40:1, 20:1, 10:1) used for film formation. Chitosan films (neat, DAS-crosslinked, DES-plasticized, and DES-plasticized/DAS-crosslinked) were obtained by solution casting, with constant total chitosan and/or Ch+DES mass across formulations, and subsequently examined in terms of molecular structure, density, mechanical characteristics, micro- and nanoscale morphology, color, wettability, and surface free energy. The most significant changes relevant to potential applications were observed in mechanical properties and surface free energy. The incorporation of DAS and DES into chitosan resulted in a significant reduction in Young’s modulus from 1150 MPa to 130 MPa, accompanied by a significant increase in elongation at break—from 10% to almost 90%. Moreover, it should be noticed that the addition of DAS and DES led to a nearly twofold increase in surface free energy, from 32.5 to 59.9 mJ m−2. While previous studies have predominantly focused on single modifications of chitosan—either covalent crosslinking with dialdehyde starch (DAS) or plasticization with deep eutectic solvents (DES)—this work introduces a pioneering dual-modification strategy that simultaneously integrates both techniques, representing the first systematic investigation of their synergistic effects unattainable through individual approaches.