MAH-g-PLA Compatibilization and ATBC Plasticization of Biodegradable PLA/PBAT Blends: A Combined Experimental and Molecular Dynamics Study

Abstract Polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends are central to biodegradable packaging. Reactive compatibilization with maleic-anhydride-grafted polylactide (MAH-g-PLA) and plasticization with acetyl tributyl citrate (ATBC) jointly toughen the 70/30 w/w blend; we resolve their combined molecular action by all-atom molecular dynamics on experimentally anchored formulations. Two Flory–Huggins χ routes straddle zero, bracketing a partial-miscibility window consistent with the two amorphous populations resolved by dynamic mechanical analysis (DMA). In the compatibilized blend the succinic-anhydride graft ring localizes on PBAT-rich regions (three-quarters of ring atoms within 0.5 nm of PBAT) while the PLA arm bridges towards PBAT (1.13× enrichment) — a polymeric surfactant consistent with the mechanical optima at 3–5 parts per hundred resin (phr). For the plasticizer, a Fox-quation mass balance of the DMA peak shifts and the simulated 0.5-nm contact statistics independently recover the same ordering: an interfacial/PBAT-associated sink fills first (≈98% of ATBC outside both phase bulks at 1 phr), and direct PLA-phase dissolution grows appreciably only near 5 phr (never exceeding 13% of molecules). At 1–3 phr ATBC anti-plasticizes by occupying free volume without creating it (fractional free volume invariant across loadings and seeds), the structural signature of the experimental ductility minimum. These cross-validated descriptors provide design rules for balancing compatibilizer and plasticizer loadings in foamable PLA blends.