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

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 x 10(4) from 21.4 x 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 degreesC, the molecular weight decreased to 3.70 x 10(4), 3.50 x 10(4) and 2.00 x 10(4) on 8 It 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 degreesC treatment, respectively. The different reaction time gave chitosan with different molecular weights. At 60 degreesC, the molecular weight of products decreased to 7.40 x 10(4) from 21.4 x 10(4) Within 4 h, then decreased slowly to 1.90 x 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. (C) 2002 Elsevier Science Ltd. All rights reserved.