Photo-thermal staged-responsive shape memory polymers prepared by fused granular fabrication 4D printing

4D printing technology is advantageous for developing new shape memory effects and new functionalities. Herein, a new type of photo-thermal staged-responsive shape memory polymer (SMP) was prepared using fused granular fabrication (FGF) 4D printing technology. The integration of an azobenzene containing oligomer (Bisdi) with commercialized thermal-responsive SMP granules (PEC) resulted in composites (PEC-Bisdi) with good compatibility and higher thermal stability, suitable for FGF 4D printing. The granules made from the composite can also be used directly in the FGF printing technology. The specimens named PEC-Bisdi printed by FGF illustrated excellent photo-thermal staged responses with ultraviolet light (UV) responsive bending, thermal-responsive shape recovery, and good fixation at room temperature. The FGF-printed specimens also displayed good mechanical properties with up to 380% elongation at break and a 1.5 GPa glassy storage modulus. The influences of material factors and printing parameters were systematically investigated and the results showed an increase in the curvature of the spline as a function of Bisdi content and elongation, while a decrease was recorded as a function of the spline thickness. The optimal printing parameters for the highest curvature were determined to be an extrusion rate of 140, an extrusion temperature of 230 degrees C, a routing rate of 80, and a parallel infill pattern. Overall, the proposed PEC-Bisdi composites showing programmable and remotely controllable shape memory capabilities have the potential for use in advanced engineering and soft robotics. Lotus leaves fabricated from PEC-Bisdi composite using FGF printing could close under UV irradiation, retain shape under visible light, and recover upon heating. After re-stretching, this photo-thermal staged-responsive procedure can be cycled.