A soft multifunctional film from chitosan modified with disulfide bond cross-links and prepared by a simple method.

Chitosan was modified with thioctic acid and used to prepare soft films. As confirmed by FTIR and XPS measurements, a condensation reaction occurred between the amino groups in the chitosan and the carboxyl groups in the lipoic acid to form amide bonds in the modified chitosan. Films were then prepared by casting at ambient conditions, and the effects of the chemical modification on the physical-mechanical, antibacterial, and thermal properties of the films were investigated. The results showed that the tensile strength, flexibility and recovery performance of the modified films were significantly different from those of the unmodified films. For example, the Young's modulus of a pure chitosan film was 2600 MPa, while the modified films were much more flexible with a Young's modulus as low as 32.5 MPa. Moreover, the modified chitosan films were not dissolved or damaged by common organic solvents or in highly acidic (pH 1) or highly basic (pH 13) conditions. The modified films also showed good antibacterial activity against both E coli and S aureus with inhibition rates of almost 100 %. These desirable properties suggest that the modified chitosan films prepared here have possible application prospects in flexible devices and packaging.