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Solvent-free solid-state foaming technology was used to fabricate microcellular polylactic acid (PLA) scaffold materials with cell sizes from 350 to 20 μm at saturation pressures of 2.5, 3.5, 4.0, and 5.0 MPa in carbon dioxide. The corresponding thermodynamic parameters were measured, including the decomposition temperature and rate, storage/loss modulus, and loss factor, using thermogravimetric analysis, dynamic thermal mechanical analysis, and scanning electron microscopy. The Kissinger, Ozawa-Doyle, and Vyazovkin equations were used to calculate the thermal decomposition kinetics for PLA foams of different cell sizes; their lifetimes in nitrogen were also obtained. It was observed that PLA foams with larger cell sizes, lower average activation energies, and better flexibilities could be fabricated at lower saturation pressures, resulting in reduced decomposition times.