Thermal Degradation and Kinetic Analysis of Pure Polyglycolic Acid in Presence of Humid Air

For the first time, thermal degradation of polyglycolic acid (PGA) is carried out in the presence of humid air. The thermal-oxidative-hydrolytic degradation of pure PGA is investigated in a batch reactor with reaction temperatures of 250°C, 260°C, 280°C, and 310°C. The effects of polymer loading and temperature on degradation are studied at different pressures (80 mmHg-760 mmHg). Degradation is carried out at different initial air partial pressures as well. It was found that degradation is enhanced considerably under higher pressures as well as higher air mole fractions. Empirical correlations were proposed to account for the effect of total pressure on degradation rate and found to be a parabolic form in respect to total pressure. The thermal- oxidative-hydrolytic degradation rate constants are evaluated within several experiments. Moreover, an optimum operational condition for reactor design features was obtained at Ptolal=102 mmHg under which the dimerization yield would be above 80%. The frequency factor and activation energy are also determined using Arrhenius equation considering both of the true and global degradation rate constants. It was found that in the presence of air, the polymer undergoes thermal-oxidative degradation with activation energy of 24-36 kcal/mol while the normal activation energy in absence of air and vapour was 24-26 kcal/mol.