Facile Synthesis of Phosphorus and Cobalt Co-Doped Graphitic Carbon Nitride for Fire and Smoke Suppressions of Polylactide Composite

Due to the unique two-dimensional structure and features of graphitic carbon nitride (g-C(3)N(4)), such as high thermal stability and superior catalytic property, it is considered to be a promising flame retardant nano-additive for polymers. Here, we reported a facile strategy to prepare cobalt/phosphorus co-doped graphitic carbon nitride (Co/P-C(3)N(4)) by a simple and scalable thermal decomposition method. The structure of Co/P-C(3)N(4) was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The carbon atoms in g-C(3)N(4) were most likely substituted by phosphorous atoms. The thermal stability of polylactide (PLA) composites was increased continuously with increasing the content of Co/P-C(3)N(4). In contrast to the g-C(3)N(4), the Polylactide (PLA) composites containing Co/P-C(3)N(4) exhibited better flame retardant efficiency and smoke suppression. With the addition of 10 wt % Co/P-C(3)N(4), the peak heat release rate (PHRR), carbon dioxide (CO(2)) production (PCO2P) and carbon oxide (CO) production (PCOP) values of PLA composites decreased by 22.4%, 16.2%, and 38.5%, respectively, compared to those of pure PLA, although the tensile strength of PLA composites had a slightly decrease. The char residues of Co/P-C(3)N(4) composites had a more compact and continuous structure with few cracks. These improvements are ascribed to the physical barrier effect, as well as catalytic effects of Co/P-C(3)N(4), which inhibit the rapid release of combustible gaseous products and suppression of toxic gases, i.e., CO.