Effects of ultrasonic conditions and storage in acidic solutions on changes in molecular weight and polydispersity of treated chitosan

The objective of this study is to explore the effects of ultrasonic conditions and storage in acidic solution on changes in the molecular weight and polydispersity (molecular weight distribution) of treated chitosan. The ultrasonic conditions studied include parameters of chitosan concentration, reaction temperature, type of solvent, and ultrasonic time. The results show that chitosan was degraded faster in dilute solutions and faster in lower temperature solutions. Degradation increased with prolonged ultrasonic time, and chitosan was degraded during storage in an acidic solution at ambient temperatures. The polydispersity decreased with ultrasonic treatment for all ultrasonic conditions studied and during storage in acidic solution. Polydispersity decreased from 10.10 to 2.11, 3.11, 4.04, and 5.09 for 0.2%, 0.8%, 1.4%, and 2.0% solutions, respectively. Polydispersity decreased to 4.04 and 4.15 for solutions treated at 4°C and 50°C, respectively. Polydispersity decreased to 4.04 and 4.31 for chitosan treated in acetic acid buffer and 5% acetic acid, respectively. Polydispersity decreased to 2.64 after prolonged (120 min) ultrasonic treatment. After storage in acetic acid buffer at ambient temperatures for 17 days, polydispersity changed from 10.10 to 6.86 for untreated and from 6.02 to 3.62, from 3.02 to 2.86, and from 2.64 to 2.34 for those chitosans subjected to ultrasonic degradation treatment for 10 min, 60 min, and 120 min, respectively.