The piperazine pyrophosphate intumescent flame retardant of polypropylene composites prepared by selective laser sintering

A highly flame‐retardant PP composite powder suitable for selective laser sintering (SLS) was prepared successfully by mechanical blending, which was composed of pure PP, piperazine pyrophosphate (PPAP), melamine polyphosphate (MPP), and triazine‐based charring‐foaming agent (CFA). The results showed that the flowability of PP composite powder decreased by about 40% and the DSC data indicated the sintering window decreased by about 2°C. Although the flame retardants influenced the processing of SLS, the PP composite powder was still able to be used for printing. The LOI value of PP composites prepared by SLS was 29.2% and the UL‐94 grade was V‐0 rating at the filler loading (16wt% PPAP, 4wt% MPP, 4wt% CFA). The cone calorimeter testing (CCT) data represented that the heat and smoke release significantly decreased. The synergistic effect among flame retardants promoted high‐quality char layers, which is favorable for improving the flame retardancy and thermal stability of PP composites by the test of TGA, SEM, Raman spectra, and FT‐IR. However, the flame retardancy and mechanical properties of PP composites made by SLS were both in varying degrees of decline compared to the ones made by thermo‐compression (TC) because of the higher porosity. An air duct with complex structures was prepared by SLS at last. A highly flame‐retardant PP composite powder especially for selective laser sintering (SLS) was prepared successfully. An air duct with flame retardancy and complex structures was printed.