Effects of inorganic fillers on the extensional rheological and morphological properties of polylactic acid/low-density polyethylene blends

Polylactic acid (PLA)/low-density polyethylene (LDPE) blends filled with hydrophilic and hydrophobic fumed silica or organoclays were characterized by linear viscoelastic (LVE) and extensional properties. LVE properties were determined using small-amplitude oscillatory shear (SAOS) tests, and morphology was determined by scanning and transmission electron microscopy analyses. Hydrophobic fillers effectively reduced the droplet size of the dispersed phase (LDPE) and improved compatibility but suppressed strain hardening in extensional viscosity. The strain hardening coefficient (SHC) used to quantify this behavior exhibited an inverse correlation with LDPE droplet size, which suggested that enhanced compatibility limited the deformability of the dispersed phase under extensional flow. The plate-like organoclays restricted droplet deformation through rigid interfacial encapsulation. These results demonstrate a trade-off between interfacial compatibility and strain hardening in the extensional viscosity of PLA/LDPE blends. This reveals that hydrophobic fillers stabilize the morphology and increase the low-frequency LVE properties at the cost of suppressed extensional strain hardening. • Hydrophobic fillers refined LDPE droplet morphology. • Filler hydrophobicity determined interfacial localization. • Compatibilization increased G′ in PLA/LDPE blends. • Organoclays suppressed extensional strain hardening. • Revealed morphology–strain hardening trade-off.