Melt and Cold Crystallization Behavior of Poly(Lactic Acid) With Different Molecular Weights and Its Influence on Mechanical, Viscoelastic, and Tribological Properties

ABSTRACT The melt and cold crystallization behavior of two PLA grades with different molecular weights was investigated using various DSC analyses. During isothermal melt crystallization, PLA with lower molecular weight exhibited faster crystallization kinetics across different temperatures. In contrast, cold crystallization was associated with a more complex behavior, being strongly dependent on the preceding cooling conditions. At higher cooling rates, PLA with higher molecular weight crystallized more rapidly from the glassy state, whereas under slower cooling conditions the trend reversed in certain cases. The effect of cold crystallization of PLA was further examined through tensile tests, dynamic‐mechanical thermal analysis (DMTA), and tribological analysis using specimens from both PLA grades, which were annealed for different durations at 110°C to achieve varying degrees of crystallinity. Tensile tests showed that the Young's modulus and brittleness increased with higher crystallinity in both PLA grades. DMTA revealed that longer annealing times resulted in higher heat distortion resistance, as evidenced by a less pronounced cold crystallization process during temperature sweeps. Moreover, tribological measurements demonstrated that controlled annealing of PLA has the potential to minimize the wear rate.