Improved Mechanical Properties of Polyurethane-Driven 4D Printing of Aluminum Oxide Ceramics.

The current deformation scheme used in the 4D printing of ceramics has several disadvantages, such as a poor deformation capacity, high process complexity, and the poor mechanical properties of the product. In order to solve these problems, the deformation scheme introduced in this study utilizes the pyrolytic expansion of polyurethane and the resulting pores to hinder the contraction of the specimen during the ceramization stage. Then, the specimen is composited with a polyurethane-free portion that has a high rate of shrinkage, and deformation is initiated through the interlayer stress mismatch generated by the difference in the shrinkage of the different layers, thus enabling the preparation of complex structural ceramics. This solution is simple and efficient; heat treatment is performed in a single pass, and the precursor specimen is highly deformable. The incorporation capacity of the aluminum oxide ceramic powder was increased by replacing part of the Dow Corning SE 1700 polydimethylsiloxane silicone rubber in the raw material with Dow Corning DC 184 polydimethylsiloxane silicone rubber, which, in turn, improved the mechanical properties of the obtained ceramics by enhancing the solid-phase content of the ceramic powder. Due to the introduction of polyurethane, the ceramic has a secondary pore structure, which has the potential for application in the field of engineering materials and heat insulation materials.