Nacre-Inspired Sustainable Polylactide/Poly(butylene adipate-<i>co</i>-terephthalate) Blends with an Excellent Strength–Toughness Balance

Nacre-inspired sustainable blends, in which polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) are alternately stacked in parallel, were fabricated by layer-assembly coextrusion. The interfacial diffusion controlled by the layer number was found to play a crucial role in optimizing the mechanical properties. With a poor interfacial diffusion at the layer number ≤32, the weak adhesion between incompatible PLA and PBAT induced multiple layer debonding and stepwise breaking during stretching, leading to a discount on the advantages of this nacre-inspired structure in integrating strength and ductility. As the layer number exceeded 128h*, the stronger interfacial diffusion triggered the formation of a thin interphase layer, which acted like an amphiphilic physical compatibilizer to bind the adjacent layers. This significantly perfected the nacre-inspired structure in PLA/PBAT blends, bringing a dramatic increase in fracture strain to 459.7% while maintaining the strength near 30.0 MPa. Moreover, the interfacial diffusion was systematically analyzed with versatile qualitative and quantitative methods, and the diffusion mechanism related to the extension–compression coupled field in coextrusion was discussed. This work provides a simple strategy for developing nacre-like structural materials with an excellent strength–toughness balance, which shows the scalability of various polymer pairs.