Surface sulfation of crab chitin for anisotropic swelling and nanodispersion

• Published in: Cellulose (London) 2022-09, Vol.29 (13), p.7099-7109
• Main Authors: Wang, Xijun, Chen, Pan, Feng, Xiao, Dang, Chao, Lin, Baofeng, Nishiyama, Yoshiharu, Qi, Haisong
• Format: Article
• Language: English
• Subjects: anisotropy; atomic force microscopy; Bioorganic Chemistry; Birefringence; cellulose; Ceramics; Chemical Sciences; Chemistry; Chemistry and Materials Science; Chitin; Composites; crabs; Cristallography; Diameters; Dimethylformamide; Fragments; Glass; homogenizers; light microscopes; Line broadening; mechanical methods; Microscopy; nanofibers; Natural Materials; Optical microscopes; Organic Chemistry; Original Research; Physical Chemistry; Polymer Sciences; Polymers; Substitution reactions; Sulfamic acid; sulfates; Sulfation; Sustainable Development; transmission electron microscopy; X-ray diffraction
• ISSN: 0969-0239; 1572-882X
• DOI: 10.1007/s10570-022-04688-2

Crab chitin was sulfated under heterogeneous conditions using sulfamic acid in N’N-dimethylformamide to selectively sulfate the microfibril surface. The degree of sulfation followed a first order kinetics assuming a limited available reaction sites on the surface, and leveled off at a bulk degree-of-substitution of 0.4, corresponding to 2 mol/kg of sulfate groups. The reaction rate was proportional to the square of sulfamic acid concentration, suggesting involvement of two sulfamic acid molecules in a reaction. When washed with water after sulfation, the crab shell chitin fragments swelled anisotropically in the helicoidal axis direction, revealing regular alternating birefringence under optical microscope. Further mechanical treatment with high-pressure homogenizer led to slender nanofibrils, whose diameters were of the order of 6 nm according to turbidimetric analysis, in agreement with the Scherrer size estimated from X-ray diffraction line broadening. Both atomic force microscopy and transmission electron microscopy measurement showed presence of further smaller fragments with diameter of 3–4 nm and contour length of 0.5–1 μ m with a few kinks. The current approach presents a rapid and efficient modification to chitin, and a strategy for the preparation of stable nanochitin suspension.