A multi-scale porous design enabling in-situ α-ZrP growth for high flame-retardant SLA-printed photopolymers

Stereolithography (SLA) is highly valued in high-end manufacturing for its exceptional design flexibility. However, the inherent flammability of photosensitive resins significantly limits their safe application. This study designed and synthesized an intrinsically flame-retardant photosensitive resin (TPH) containing phosphorus and sulfur elements. The TPH resin was blended with a phosphorus-containing reactive diluent and an ionic liquid (TFS) to prepare a photosensitive resin (TPHP) suitable for SLA technology. An innovative approach was employed where macroscopic pore structures were constructed through 3D printing, and due to phase separation between the ionic liquid and the 3D-printed samples, microscopic pores were incorporated within the SLA-printed specimens, a porous framework was formed. These pores served as reaction sites for in-situ growth of a nano-zirconium phosphate (α-ZrP) layer on the surface. Thermogravimetric and flame retardancy tests demonstrated that the incorporation of α-ZrP significantly enhanced the material's thermal stability, flame retardancy, and smoke suppression properties. Compared with unmodified samples, the char residue was increased to 47.3%, the limiting oxygen index reached 29.0%, and the UL-94 rating achieved V-0. Cone calorimetry tests showed reductions in peak heat release rate, total heat release, and total smoke production by 42.1%, 65.4%, and 75.1%, respectively. The results indicate that this work provides a new strategy for flame-retardant 3D printing. It resolves the intrinsic conflict between flame retardancy and printability by combining surface pore engineering with in situ growth to achieve surface functionalization without sacrificing printability.