Chitosan is an attractive biopolymer derived from shrimp shells that has a propensity to form plastics and films. Because chitosan plastics are generally fragile and brittle, small molecules known as plasticizers are commonly introduced to improve flexibility. Glycerol is the most widely used plasticizer for chitosan. And while chitosan plastics have been extensively studied in the laboratory, there remains a lack of understanding of the interactions between chitosan and the glycerol on a molecular level. Here, we describe an in-depth spectroscopic study into the intermolecular interactions between the monomeric repeat unit of chitosan, glucosamine, and glycerol. We used infrared and nuclear magnetic resonance spectroscopy in combination to investigate glucosamine assembly and establish diagnostic signals for intra- and intermolecular glucosamine interactions. We have found that the addition of glycerol to glucosamine leads to a disruption in intramolecular glucosamine-glucosamine hydrogen bonds and the promotion of glucosamine self-assembly. Furthermore, we observed a significant preference for glycerol binding to the amine functionality of glucosamine. Insights from these studies have been applied to probe other polyol-based plasticizers and explore the feasibility of employing additives to yield responsive and tunable plasticizers. This work has provided a detailed and unique perspective into glucosamine-polyol interactions and the plasticization of chitosan and other polysaccharide-based biopolymers.

Glucosamine as a model for probing molecular level interactions in chitosan bioplastics

ACS Spring 2022

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