Revisiting the Effect of Constructing Stereocomplex Crystallites through a Compatibilizer in Super Tough PLLA Blends

The investigation focused on understanding the toughening effect in poly(l-lactide) (PLLA) blends achieved by forming interfacial stereocomplex (SC) crystallites after prereacting a compatibilizer with poly(d-lactide) (PDLA), as reported in the previous study. After the ungrafted fraction was removed, the grafted PDLA content was determined to be 24.5 wt %. These interfacial SC crystallites (formed by grafted PDLA with PLLA) created a “rigid” interface that stabilized poly(butylene adipate-co-terephthalate) (PBAT) particles, maintaining a sea–island morphology. In contrast, free SC crystallites (formed by ungrafted PDLA with PLLA) acted as rheology modifiers, inducing a cocontinuous structure. The notched impact strength of the interfacial SC crystallite-modified PLLA/PBAT blend was 7.2 kJ/m2, significantly lower than the 47.6 kJ/m2 achieved with free SC crystallites. Most notably, it was demonstrated that the cocontinuous structure was caused by the coalescence of PBAT particles, and increasing the content or mixing time of PDLA was crucial for improving the cocontinuous structure, thereby achieving high toughening efficiency.