Facile route to tri-carboxyl chitin nanocrystals from di-aldehyde chitin modified by selective periodate oxidation

Chitin, a kind of polysaccharide mainly obtained from food waste, has emerged as an important biodegradable biopolymer in composite materials. The difficulty of aldehyde modification, which greatly limited the application of chitin nanocrystals, was addressed by applying a facile route of partial deacetylation followed by periodate oxidation in this study. Deacetylation occurred on the surface of both crystalline and amorphous regions, which were significantly degraded in the following periodate oxidation due to the inevitable cleavage of chitin chains, leading to an increase in the crystallinity index of obtained di-aldehyde chitin. The degree of deacetylation and periodate addition had limited improvement in the aldehyde content of di-aldehyde chitin with a maximum value of around 0.42 mmol/g. With further 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidation, the carboxyl content of tri-carboxyl chitin was improved to 1.58 mmol/g, which played a critical role in the dispersion efficiency and morphology of chitin nanocrystals. The obtained rod-like chitin nanocrystals with a ζ-potential value of -42 mV and an average size of 97 nm have potential application in dye-adsorption and emulsion stabilizers.