Highly-efficient method for chitin nanocrystal production using solid-state phosphoric acid hydrolysis

A facile, efficient, and high yield method for producing chitin nanocrystals (ChNCs) using ultrasound-assisted phosphoric acid (PA) hydrolysis was developed. The hydrolysis was conducted at high chitin loading of 40 wt% and at a mild temperature of 50 °C, with the chitin-PA mixture remaining in a solid paste-like form throughout the reaction. The ChNCs produced showed an average length of ~ 200 nm and a cross-section of ~ 20 nm. Three reaction conditions were compared, at PA concentrations of 65, 75, and 85 wt%. Negligible changes in the sizes of ChNCs and degree of acetylation (DA) of the chitin (~ 96%) were observed, while the ChNC yield varied from 75.1 wt% at 65 wt% PA concentration to 49.6 wt% at 85 wt% PA concentration. The ChNCs were weakly charged, with a ζ-potential of ~  + 27 mV, owing to the inherent deacetylated N-acetyl groups. Overall, ultrasound-assisted PA processing provides an efficient and relatively environmentally-benign method for ChNC production.