Effects of the Three-Phase Crystallization Behavior on the Hydrolysis of Amorphous and Semicrystalline Poly(lactic acid)s

The hydrolysis of poly(lactic acid), PLA, was investigated considering the changes in the three-phase model structures, the mobile amorphous, crystalline (CF), and rigid amorphous fractions (RAF). Amorphous PLA films with different l-lactide were crystallized by cold-crystallization and melt-stretching crystallization to promote the three-phase structural variation in the PLA films. The changes in the phase structure and molecular weight during hydrolysis were investigated. As a result, PLA with higher CF had a slow hydrolysis rate due to limited water diffusion into the crystalline structure. Conversely, the initial amount of RAF fasten the hydrolysis affected by the higher water diffusion and more hydrophilic end groups at the early stage. Moreover, the distinct structure of the nanoconfined crystals from the melt-stretching method could limit the diffusion of water molecules into the PLA film and accordingly add more stability to the hydrolysis.