Preparation and Structural Investigation of Novel β-Chitin Nanocrystals from Cuttlefish Bone

Novel β-chitin nanocrystals (β-CNCs) were extracted from cuttlefish bone via deproteinization and demineralization, followed by acid hydrolysis. As a new source of β-chitin, β-CNCs obtained from cuttlefish bone were bumpy and relatively spherical in shape, whereas α-CNCs extracted from shrimp shell had a rod-like-shape. Also, the average width and length of β-CNCs were 14 and 22 nm, respectively, whereas the average dimensions of α-CNCs were 26 nm (diameter) × 320 nm (length). The differences in shape and dimensions between β-CNCs and α-CNCs might originate from the different chitin microfibrillar structures within the hierarchical multilayers with calcium carbonate, called a Bouligand structure, in shrimp shell or cuttlefish bone. From the NMR spectra, the DD values of purified α-CNCs and β-CNCs were found to be 17% and 13%, respectively. From the XRD patterns, the complete transformation of β-CNCs to α-CNCs was observed during the acid hydrolysis. By contrast, β-CNCs had higher surface areas due to their smaller sizes and better dispersity in water suspension without aggregation. Furthermore, the deacetylation of β-CNCs was induced by a concentrated NaOH solution. The structural and thermal properties of the β-CNCs and deacetylated β-CNCs were characterized through proton nuclear magnetic resonance (¹H NMR), transmittance electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC).