Effect of reaction temperature and reaction time on the preparation of low-molecular-weight chitosan using phosphoric acid

Abstract Low-molecular-weight chitosan were prepared using 85% phosphoric acid at different reaction temperatures and reaction time. At room temperature, the viscosity average-molecular weights ( M v ) of chitosan decreased to 7.1×10 4 from 21.4×10 4 after 35 days treatment. The degradation rate decreased with increasing hydrolysis time. The yields of chitosan also continuously decreased from 68.4 to 40.2% after 35 days. At 40, 60 and 80 °C, the molecular weight decreased to 3.70×10 4 , 3.50×10 4 and 2.00×10 4 on 8 h hydrolysis, respectively. The yields of chitosan remain at a high level compared with that at room temperature and were 86.5, 71.4 and 61.3% at 40, 60 and 80 °C treatment, respectively. The different reaction time gave chitosan with different molecular weights. At 60 °C, the molecular weight of products decreased to 7.40×10 4 from 21.4×10 4 within 4 h, then decreased slowly to 1.90×10 4 in 15 h. It was also found that the water-solubility of chitosan increased as the molecular weight decreased. Results show the changes in yields and molecular weight of chitooligomers were strongly dependent on the reaction temperature and reaction time.