Modeling the pH-dependent PLA oligomer degradation kinetics

The hydrolysis of lactic acid oligomers involves several different reactions, acid-catalyzed, base-catalyzed as well as non-catalyzed. In the present paper a pH-dependent kinetic model has been developed and its kinetic constants evaluated by fitting to experimental data of degrading lactic acid oligomers at 37 °C in aqueous solution at pH = 1, 2, 3.5, 5.7 and 7.4. The model was able to properly describe the experimental data with an average error of about 5%. The estimated values of the kinetic constants at the selected temperature are: kDα=4.44×10−3 L2mol−2h−1, kDβ=9.29×10−4 L2mol−2h−1 (acid-catalyzed), kRH=1.56×103 L2mol−2h−1, kBB=2.88×106 Lmol−1h−1 (base-catalyzed) and kW=2.49×10−5 Lmol−1h−1 (non-catalyzed).