Tuning the dual- and triple-shape-memory effect of thermoplastic polyurethane/polylactic acid/poly(propylene carbonate) ternary blends via morphology control

In this work, the ternary shape-memory blends consisting of thermoplastic polyurethane (TPU), polylactic acid (PLA), and poly(propylene carbonate) (PPC) were prepared via direct melt blending. Due to the different compatibility, viscosity and surface tension, PLA and PPC coalesce into a compound phase (LPC) and then assembled with TPU to form a special co-continuous structure in each blend as the mass ratio of TPU and LPC fixed at 50:50, which was first predicted based on the spreading coefficient theory and then confirmed by SEM observation. Moreover, the morphology of PLA and PPC serving as switches and the interfacial area between TPU and LPC can be tailored through simply adjusting the composition of LPC, leading to the tunable dual- and tripleshape-memory effects (DSME and TSME). For DSME via regarding the whole LPC as the single switch, both the shape fixation and recovery ratios decline with decreasing the PLA content. It is revealed that replacing PLA with PPC not only weakens the mechanical support from LPC for holding temporary deformation but also reduces the interfacial area and thus the driving effect from TPU for shape recovery. When PLA and PPC respectively act as the switch to memorize the two temporary shapes, TSME can be realized and the property governed by phase morphology exhibits diverse variation trends at the different stages. By comparison, the blend containing 15 wt% PLA showed the best TSME, which was characterized both qualitatively and quantitatively. The simplicity of this strategy in fabricating polymeric materials with tunable multiple-shape-memory performances implies the scalability to other polymer pairs.

Automated summary

In this study, ternary shape-memory blends consisting of TPU, PLA, and PPC were prepared via direct melt blending. The composition of LPC can be adjusted to tailor the morphology of switch PLA and PPC and the interfacial area between TPU and LPC, resulting in tunable dual- and triple-shape-memory effects. The blend containing 15 wt% PLA showed the best TSME, characterized both qualitatively and quantitatively.