Abstract: For utilizing the main components of the mulberry branch effectively and obtaining acetylated products with low degraded degree, the method of two-step acetylation was carried out under the relatively mild condition. At the first step, the acetylated product(AS₁) was obtained after 3 h at 80 ℃, and the quality ratio of sulfuric acid, acetic anhydride and acetic acid with the raw material was 1:8, 25:2 and 10:1, respectively. At the second step, the acetylated product(AS₂) was obtained after 4 h at 90 ℃, and the quality ratio like the above was 1:20, 15:2 and 15:2. The results showed that the yield of the acetylated product by two-step was 112.60%, the intrinsic viscosity was 71.09 mL/g and its initial degradation temperature was 175 ℃. They were all superior to those by the trifluoroacetic-acid method and high-temperature method. Fourier transform infrared spectroscopy (FT-IR) of the product by two-step acetylated showed that the signals corresponding to acetyl were identified. Thermogravimetric analysis(TGA)showed that the product started to degrade at 175 ℃ and differential scanning calorimeter (DSC) results revealed that the glass transition point was 160 ℃.

Key words: mulberry branch, low degradation, two-step method, acetylation