Tailored Mechanical Properties of the Poly(L‐Lactic Acid) Lattice Structure by Polymorphic Isothermal Crystallization Kinetics Control During Laser Powder Bed Fusion Process

The properties of poly(L‐lactic acid) (PLLA) are strongly influenced by its polymorphic crystal structures. This study investigates the isothermal crystallization behaviors of PLLA during the laser powder bed fusion (LPBF) process and establishes the correlations with the mechanical properties of the PLLA lattice. It is found that the evolution of PLLA crystal polymorphs exhibits a strong dependence on the powder bed temperature ( ). A dual‐Avrami model is developed to predict the isothermal crystallization kinetics of PLLA, successfully describing the primary and secondary crystallization stages with prediction errors confined within −0.072 to 0.025. Meanwhile, a crystallization‐free threshold model is first proposed to extrapolate and identify 130°C as the practically optimal within the processable window. At 130°C, the grain sizes (homogeneous crystallization size) and (normal crystallization size) of the α phase reach 56.58 and 26.51 nm. Compared to the baseline at 101°C within the actual sintering window, the crystallinity increases from 23.46% to 34.93%. Correspondingly, the compressive strength and Young's modulus exhibit remarkable enhancements of 387.09% and 362.23%, respectively. A framework is established to correlate the evolution of / phase under varying with tailored mechanical responses. This paper lays the groundwork for optimizing the crystal structure‐processing‐properties relationship of personalized PLLA scaffolds.