Synthesis of unsaturated polyurethane oligomer and its application in the 3D printing of composite solid propellants

Propellants are the main source of energy for internal ballistic processes. The use of 3D printing technology is expected to produce propellants with complex geometries. However, limited by the properties of existing printable resins, the mechanical properties of 3D-printed propellants make it difficult to meet the requirements for use. This study deals with the structural design, synthesis, and properties of an unsaturated polyurethane resin (PUA). A photoinitiator was added to this polyurethane resin and a photo-curable elastomer was successfully prepared under UV irradiation with tensile strength and elongation at break of 21.06 MPa and 1119 %, respectively. Then, the resin was mixed with active diluent, initiator, NH4ClO4, and Al particles to prepare the propellant slurry, and the rheological properties of the slurry were investigated. The results show that the propellant pastes have good flowability at 40 °C and are suitable for 3D printing. Finally, solid propellant and insulation samples with complex structures were effectively generated using UV-curable 3D printing technology, in which the tensile strength and elongation at break of the propellant samples were 0.923 MPa and 63.2 %, respectively. The fabrication of the grains with high precision and performance demonstrated the feasibility of the PUA binder in the 3D-printed propellant.