Optimal conditions for preparation of low molecular weight chitosan with sonolysis were described.The influence of sonolysis conditions and the molecular parameters of initial chitosan on the degradation rate and degradation rate constant was investigated in detail.Weight-average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of samples were measured by gel permeation chromatography.The structure of degraded chitosan was characterized by Fourier transform infrared spectroscopy and X-ray diffraction.For a given sonolysis time

the decrease in molecular weight has been found to be the greatest at the lowest reaction temperature and lowest chitosan concentration.Molecular weight of samples decreased exponentially with increasing sonication time at early stages.The action mode of ultrasound on the splitting of molecular chains of chitosan was discussed.The degree of deacetylation of the main hydrolysis products almost unchanged compared with the initial chitosan.The decrease of molecular weight led to transformation of crystal structure

but the chemical structures of residues were not modified.Ultrasonic treatment on chitosan is an alternative

safe method to prepare different molecular weight chitosan which is more suitable for biomedical and food applications.