Chemiluminescence kinetic analysis on the oxidative degradation of poly(lactic acid)

The oxidation of polymers is characterized by the generation of free radicals, and the kinetic parameters depicting the progress of oxidation are specific for each material structure and formulation. The durability of materials depends intrinsically on the molecular structure, and degradation mechanism influences the long-term stability of products. The intimate transformations of macromolecules can be reliably characterized by chemiluminescence (CL), which depicts the evolution of oxidation state by the reaction of free radicals with molecular oxygen. The isothermal and nonisothermal CL spectra are complementary proofs for the interpretation of oxidation behavior involving hydroperoxide as the initiators of oxidation. The degradation of PLA takes place by decomposition and fragmentation to lactide. The values of five kinetic parameters (initial CL intensity, CL intensity at the first peak, temperature corresponding to the first peak, oxidation induction time and oxidation rate) obtained for oxidative degradation of PLA lead to the activation energies ranged between 49 and 99 kJ mol(-1). The evolution of thermal degradation for poly(lactic acid) is an excellent example for the explanation of the decay fate of radical intermediates.