Abstract: Chitosan (CS) was dissolved with the aid of ultrasound and hydrogen peroxide treatment. Then, sodium tripolyphosphate (TPP) was introduced as a crosslinker into CS solution from bottom to top. Finally, chitosan microflower (CSMF) was obtained by collecting the resulting precipitate and freeze-drying it. CSMF was characterized and the factors affecting its formation were studied. The results showed that the size of CSMF was 1–2 μm in diameter. The Fourier transform infrared (FTIR) spectrum of CSMF showed a vibration peak of phosphate group at 532 cm-1. The crystal form of CS changed from semi-crystalline structure to hydrated polycrystalline structure after conversion into CSMF. X-ray photoelectron spectroscopy (XPS) showed that CSMF produced C-N＋ bond, and thermogravimetric analysis (TGA) showed that the thermal stability of CSMF was slightly lower than that of CS. Also, it was found that pretreatment method, ultrasonic time, CS solution temperature and CS/TPP ratio (m/m) but not ultrasound power or hydrogen peroxide addition could affect the flower-shaped structure of CSMF. Furthermore, it was inferred that the formation mechanism of CSMF was related to that fact that after the degradation of CS into short- or long-chain CS within a certain molecular mass range, relatively longer and shorter degraded CS chains were crosslinked by TPP to respectively form the pedestal of the microflower structure and nanosheets which were self-assembled on the substate through the interaction between the –NH3+ and phosphate ions in the structure of CS.

Key words: chitosan; sodium tripolyphosphate; chitosan microflower