Fundamentals\nof Toughening Core–Shell Bioplastic\nMaterials from a Molecular Perspective

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