Preparation and structural analysis of chitosan films with and without sorbitol

•Chitosan is environmentally friendly and sorbitol is widely used as a plasticizer.•Acetic acid cracks chitosan bonds, enabling sorbitol to enter and form hydrogen bonds.•Chitosan films made with sorbitol have a homogenous and smooth appearance.•Sorbitol is miscible with chitosan and can act as a good crosslinking agent.

The purpose of this study was to clarify the structural changes in chitosan films made with sorbitol. The degree of deacetylation (DD) in the starting chitosan was 85% or 95%. The appearance and cross-sectional characteristics of the films were analyzed by SEM. This showed sorbitol to be a good crosslinking agent, generating the desired miscibility with both types of chitosan. XRD revealed an increase in crystallinity for films without sorbitol and a decrease for films spiked with sorbitol compared with the original chitosan. FT-IR showed that the addition of sorbitol did not change the chemical structure of chitosan and no new types of bonds were created during film formation. Changes in the chemical surrounding of carbon atoms analyzed by CP/MAS 13C NMR indicated that the acetic acid solution used partially destroyed the chitosan powder and protonized some groups, enabling sorbitol to be inserted and to form hydrogen bonds in the matrix.

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