Fabrication of thermoplastic polyurethane/polylactide shape-memory blends with tunable optical and mechanical properties via a bilayer structure design

Herein, the shape-memory polymeric materials (SMPs) with tunable morphological structures were fabricated via a bilayer structure design. The bilayers containing pure thermoplastic polyurethane (TPU) and pure polylactide (PLA) and pure TPU and co-continuous TPU/PLA blend (PTB) were produced by hot laminating, which transformed the sea-island structure in conventional blend into special co-continuous structures without compositions changing. The shape fixity and shape recovery ratios dramatically increased from 77.0% to 82.9% of the blend to 99.4% and 83.4% of TPU/PTB bilayer and 99.4% and 89.1% of TPU/PLA bilayer, even larger than those of the co-continuous structured blend. The enhanced phase continuity along the deformation direction and the strong shearing effect between two layers optimized the temporary shape fixation and the permanent shape recovery. Particularly, the bilayer assembly endowed the TPU/PLA bilayer with optical transparence, while the dispersed PLA resulted in an opacity of the TPU/PTB bilayer and the conventional blend. In addition, the TPU/PLA bilayer realized balanced tensile strength and ductility via maximumly optimizing the synergistic effect of two components in mechanical properties. This work provides a promising method to fabricate transparent SMPs with balanced mechanical performances, which can be extended to other material combinations.