Rheology-Guided PHB/PBAT/MgO Nanocomposites for FDM Printing with Balanced Mechanical and Degradation Performance

Biodegradable poly-(3-hydroxybutyrate) (PHB)/poly-(butylene adipate-co-terephthalate) (PBAT) blends are promising for fused deposition modeling (FDM), but their application is limited by phase immiscibility and inadequate melt stability. This study investigates the effects of reactive compatibilization with Joncryl ADR and MgO nanoparticle incorporation on the rheological behavior, FDM processability, mechanical performance, thermal behavior, morphology, and degradation of PHB/PBAT blends. Reactive compatibilization increased melt elasticity, complex viscosity, and relaxation time, accompanied by improved filament stability and FDM printability. The PHB/PBAT/J0.3 formulation exhibited the best mechanical performance, reaching a tensile strength of 17.73 MPa, an elongation at break of 705%, and a toughness of 78.66 MPa, corresponding to increases of approximately 86, 45, and 116%, respectively, relative to the uncompatibilized PHB/PBAT (25:75) blend. Thermal and morphological analyses showed formulation-dependent changes in crystallization, thermal stability, and phase morphology, while MgO incorporation influenced both mechanical and degradation behavior. In vitro testing in phosphate-buffered saline at 37 °C showed progressive degradation over 42 days. Overall, the results demonstrate that controlling melt viscoelasticity through reactive modification provides a practical route to balancing FDM processability, mechanical performance, and degradation behavior in biodegradable PHB/PBAT-based materials.