High-performance nanostructured shape-memory polymer blends developed via solid-state mixing

Multiple-shape memory polymers (MSMPs) require hierarchical architectures capable of efficiently storing and releasing elastic energy through distinct permanent and switching domains. In this work, we test the hypothesis that nanoscale homogeneous polymer blends possessing molecular-level heterogeneity—created via solid-state mixing—can achieve high-efficiency dual- and triple-shape memory effects through the cooperative action of crystalline domains and polymer–polymer interphases, even without chemical crosslinking. To verify this hypothesis, semicrystalline–semicrystalline (PBT/PLA), semicrystalline–amorphous (PBT/PETG), and fully amorphous (ABS/a-PET) polymer blends were prepared by conventional melt mixing and by high-pressure torsion (HPT) solid-state mixing, and their shape-memory behaviour was systematically compared. Solid-state mixed blends form a single nanoscale homogeneous amorphous phase while retaining molecular-level heterogeneity, resulting in a broadened glass-transition interval. The HPT-processed PBT/PLA and PBT/PETG blends exhibit outstanding dual- and triple-shape memory performance, with shape fixity ratios R f ≈ 95–96% and recovery ratios R r ≈ 90–94%, showing negligible degradation (<2%) over multiple programming–recovery cycles. Even the fully amorphous ABS/a-PET system demonstrates a pronounced improvement, achieving Rf ≈ 90–92% and R r ≈ 82–84%, approaching the threshold of practical shape-memory performance. In contrast, immiscible melt-mixed counterparts show significantly lower values ( R f ≤ 75%, R r ≤ 66%) and poor cyclic stability. These results demonstrate that crystalline domains act as universal physical permanent domains for all amorphous chains in the homogeneous phase, while interphase regions generated by solid-state mixing function as additional morphological permanent domains that enhance mechanical coupling and suppress creep. The combination of nanoscale homogeneity and molecular-level heterogeneity enables stable, temperature-dependent multi-shape programming. This study establishes interphase engineering and crystalline-amorphous cooperativity via solid-state mixing as a robust and scalable strategy for designing high-performance, recyclable multi-shape memory polymer systems.