Preparation, structure and crystallinity of chitosan nano-fibers by a solid–liquid phase separation technique

Chitosan acetate nano-fibers were fabricated via a solid–liquid phase separation technique. The chitosan acetate structure was influenced by phase separation temperature, chitosan concentration and acetic acid concentration. Uniform nano-fibrous chitosan acetate of 50–500 nm in diameter was engineered at 0.05% (w/v) chitosan and 0.025% (v/v) acetic acid in liquid nitrogen, as opposed to film-shape and micro-fibrous structure at −18 °C and −80 °C respectively. Decreasing the chitosan concentration led to the formation of nano-fibrous/floccules-like structure, while increasing the acetic acid concentration resulted in nano-/micro-fibrous structure instead. The chitosan acetate structure was closely related to the crystallinity varying with different phase separation conditions. Nano-fibrous chitosan acetate showed a medium crystallinity with a glass transition temperature of 155.1 °C and a heat capacity of 29.1 J/g comparing with nano-fibrous/floccules-like and nano-/micro-fibrous samples. The chitosan acetate crystal was also found changeable from form I to form II after solid–liquid phase separation in liquid nitrogen.