Breaking the $$\:{\varvec{T}}_{\varvec{g}}$$ barrier in 4D printing: ultra-high temperature GF/TPI shape memory composite

Abstract Integrating 4D printing with high-performance thermoplastic polyimide (TPI) offers significant potential for developing adaptive/self-deployable structures for extreme environments. However, processing TPI through fused filament fabrication (FFF) remains challenging due to its elevated melt viscosity and high melting temperature. In this work, glass fiber (GF) reinforced TPI (GF/TPI) composites are developed for ultra-high-temperature 4D printing applications. Firstly, the GF/TPI composite is developed through melt-mixing, followed by filament preparation and 3D printing. Printed specimens are subsequently post-processed and systematically characterized for microstructural and shape-memory properties to evaluate their suitability for high-temperature 4D printing. Microstructural analysis confirmed uniform material deposition, strong fiber-matrix interfacial bonding, and good printing integrity, validating selected processing parameters. The 4D printed GF/TPI composite showed excellent shape-memory behavior, exhibiting a shape fixity ( $$\:{R}_{f}$$ ) of 93.33% and shape recovery ( $$\:{R}_{r}$$ ) of 98.70% in the first cycle, which further decreased to 91.62% and 90.19% in the tenth cycle. A reduction of 8% in the $$\:{R}_{r}$$ across the successive ten cycles is observed, indicating good cyclic stability of the shape memory effect (SME). The comparative study demonstrated superior shape-memory performance of the developed GF/TPI composite compared with existing high-temperature polymer systems under repeated cycles. The 4D-printed GF/TPI soft robotic gripper demonstrated excellent dimensional accuracy, surface finish, and stable actuation, confirming its suitability for deployable structures in space.