Individual chitin nano-whiskers prepared from partially deacetylated α-chitin by fibril surface cationization

Abstract

α-Chitin was partially deacetylated to degrees of N-acetylation (DNAc) 0.74–0.70 by 33% NaOH treatment at 90 °C for 2–4 h. Solid recovery ratios or yields of the products were 85–90%. Crystallinity index and crystal size of the original α-chitin were maintained, showing that the partial deacetylation mostly occurred on the α-chitin crystallite surfaces. Transparent and highly viscous liquids were obtained by disintegration of the partially deacetylated chitins in water at pH 3–4. Transmission electron microscopy (TEM) revealed that the liquids consisted mostly of individual nano-whiskers with average width and length 6.2 ± 1.1 and 250 ± 140 nm, respectively. Some α-chitin nano-fibrils of more than 500 nm in length were also detected in TEM images. Because the DNAc values 0.74–0.70 correspond to 1.34–1.56 mmol g −1 C2-amino group contents, high cationic charges might be formed on the α-chitin fibril surfaces in high density by protonation in water at pH 3–4.