Molecular Weight–Dependent Stereocomplex Crystallization, Thermal Stability, and Mechanical Performance of PLLA / PDLA Blends Plasticized With Epoxidized Soybean Oil: Experimental Characterization and Finite Element Validation

ABSTRACT Stereocomplex polylactic acid (SC‐PLA), formed by blending poly(L‐lactic acid) (PLLA) and poly(D‐lactic acid) (PDLA), offers superior thermal and mechanical properties over homopolymeric PLA. However, the influence of molecular weight combination on stereocomplex formation and the resulting performance remains insufficiently understood. This study systematically investigates the effects of combining PLLA (M w = 125–209 kg/mol) and PDLA (M w = 113–150 kg/mol) at a fixed 50:50 blend ratio with 10 wt% epoxidized soybean oil (ESO) as a plasticizer. Differential scanning calorimetry (DSC) revealed that lowering the molecular weight of both components promoted SC crystallization, with the SC selectivity (f c,sc ) increasing from 0.46 to 0.96 and SC crystallinity (X sc ) reaching 47%. Thermogravimetric analysis (TGA) confirmed a positive correlation between X sc and thermal stability, with initial decomposition temperatures improving by up to 25.6°C. Tensile testing uncovered a critical crystallinity–ductility balance: while samples with X sc ≈47% were too brittle to test, the L130D120 formulation (X sc = 13.68%) achieved an elongation at break of 36.4%. Dynamic mechanical analysis (DMA) confirmed that molecular weight–dependent chain entanglement directs room‐temperature stiffness. Finite element analysis (FEA) using an elastoplastic constitutive model reproduced experimental tensile behavior within 5% error. These findings establish quantitative structure–property relationships and provide design guidelines for tailoring SC‐PLA properties through molecular weight selection.