Preparation of flame-retardant polyamide 6 by incorporating MgO combined with g-C3N4

Flame-retardant polyamide 6 (PA6) was prepared by an inorganic-organic composite (MCN or MgO/g-C3N4) synthesized by incorporating magnesium oxide (MgO) combined with graphitic carbon nitride (g-C3N4). As compared to g-C3N4, MCN possessed a laminate structure, more holes, and a larger specific surface area. The addition of MCN could effectively improve the flame retardancy and mechanical properties of PA6 due to its better compatibility and dispersion in the PA6 matrix. When the addition of MCN was 20 wt%, the vertical combustion performance of the PA6/MCN sample reached flammability rating V-0 (UL-94) and the limiting oxygen index (LOI) was up to 32.1%. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed that the introduction of MCN efficiently enhanced thermal stability of PA6. The morphologies of the char residue observed by scanning electron microscopy (SEM) verified that MCN promoted the formation of sufficient, compact, and homogeneous char layers on the composite's surface during burning. Thus led to increase the char layer strength and improve the flame retardancy of PA6. The thermogravimetric analysis/infrared (TG-IR) revealed the gas-phase retardancy mechanism of MCN. Compared with PA6/g-C3N4, PA6/MCN showed better mechanical properties in terms of flexural strength and tensile strength.