Evaluation of kinetics parameters for poly(l-lactic acid) hydrolysis under high-pressure steam

In order to evaluate more precise kinetics parameters: rate constant k and Ea values for poly(l-lactic acid) hydrolysis, the reaction was carried out under high-pressure steam in a temperature range of 100-130 °C. Molecular weights of hydrolyzates were calculated by the universal calibration method without being influenced by any weight loss. The changes in molecular weight could be successfully explained according to the auto-catalytic hydrolysis mechanism, clearly indicating the critical point. Resulting k and Ea values were estimated as 8.4 × 10−5-7.2 × 10−4 s−1 and 87.2 kJ mol−1 with high R2 values, respectively. Moreover, to determine the deviation of the parameter values, influences of four factors on the measurements and calculation: (1) use of number-average molecular weight value alone, (2) use of relative molecular weight based on polystyrene standards, (3) weight loss during the hydrolysis, and (4) selection of reaction mechanism were evaluated quantitatively.