Fabrication and characterisation of α-chitin nanofibers and highly transparent chitin films by pulsed ultrasonication

α-Chitin nanofibers were fabricated with dried shrimp shells via a simple high-intensity ultrasonic treatment under neutral conditions (60   KHz, 300   W, pH   =   7). The diameter of the obtained chitin nanofibers could be controlled within 20–200   nm by simply adjusting the ultrasonication time. The pulsed ultrasound disassembled natural chitin into high-aspect-ratio nanofibers with a uniform width (19.4   nm after 30   min sonication). The EDS, FTIR, and XRD characterisation results verified that α-chitin crystalline structure and molecular structure were maintained after the chemical purification and ultrasonic treatments. Interestingly, ultrasonication can slightly increase the degree of crystallinity of chitin (from 60.1 to 65.8). Furthermore, highly transparent chitin films (the transmittance was 90.2% at a 600   nm) and flexible ultralight chitin foams were prepared from chitin nanofiber hydrogels.