A simple and rapid Fourier transform infrared method for the determination of the degree of acetyl substitution of cellulose nanocrystals

The application of cellulose nanocrystal (CNC) is limited by the rich hydroxyl groups on its surface. It can be promoted by acetylation. The degree of acetyl substitution of CNC is a key index to evaluate its performance. In this paper, a series of acetylated CNC with different degrees of substitution (DS) were prepared by acetylation with acetic anhydride and were analyzed by means of Fourier transform infrared spectroscopy (FTIR). The absorbance ratio (AR) of the band at ~ 1745 cm−1 to the one at 1164 cm−1 was applied to determine the DS. An excellent linear relationship with a correlation coefficient \( R^{2} \ge 0.994 \) between AR and the referenced DS from 1H NMR was established. The regression equations, both based on band area ratio and band height ratio, can be directly applied to any FTIR instruments. The proposed method is simple, rapid and universal and can also be applied to determine the DS of any other cellulose derivatives.