Fundamentals of Toughening Core-Shell Bioplastic Materials from a Molecular Perspective

This study analyzed the fracture behavior of poly(lactic acid) (PLA)/polybutylene succinate (PBS)/thermoplastic starch (TPS) blends featuring nanoscale-dispersed core-shell structures using molecular dynamics (MD) simulations, elucidating the toughening mechanisms at the molecular-level. Four models (PLA/TPS25, PLA/PBS/TPS5, PLA/PBS/TPS25, and PLA/PBS/TPS50) with varying core-shell structure parameters were utilized in the MD simulations. The fracture energy relationship obtained from the deformation simulation was PLA/PBS/TPS25 > PLA/PBS/TPS5 > PLA/PBS/TPS50 ≈ PLA/TPS25, which generally reproduced the experimental results of the impact test of the blends. The entire material was fractured by delamination at the TPS/PLA interface in the PLA/TPS25, and at the TPS/PBS interface in the PLA/PBS/TPS50 with the thinnest PBS shell. The PLA/PBS/TPS5 with the thickest PBS shell exhibited a reduced toughening effect due to the formation of numerous voids in the PLA matrix phase during deformation. In PLA/PBS/TPS25 with an intermediate thickness PBS shell, moderate-density voids formed during deformation, releasing strain constraints and effectively strengthening the material. The orientation hardening of PLA and PBS that occurs during deformation also contributes to the deformation energy absorption of PLA/PBS/TPS25. The molecular-level toughening mechanism elucidated in this study is anticipated to contribute to the enhancement of the properties of a wide range of bioplastics containing polysaccharides.