Preparation of a novel supramolecular intumescent flame retardants containing P/N/S/Fe/Zn and its application in polylactic acid

A novel integrative supramolecular intumescent flame retardant was fabricated by self-assembly of melamine, paminobenzene sulfonic acid and phytic acid and was abbreviated as MAP. After chelation with Fe3+ or Zn2+, the resulted products (MAP-Fe and MAP-Zn) were melt-blended with polylactic acid (PLA) to enhance the flame retardancy of PLA. The fire performance was characterized by limiting oxygen index (LOI), UL-94 vertical burning and cone calorimeter tests. The results showed that control PLA was flammable with a low LOI of 20.4%, and it cannot satisfy any UL-94 grade for its severe ignited dripping, whilst the incorporation of 3% MAP-Zn increased the LOI to 29.2%, upgraded the UL-94 rating to V-0, and reduced the peak heat release rate by 18.7%. It was proposed that MAP-Zn mainly promoted the formation of more graphitic carbon in the char residues. In addition, the presence of 3% MAP-Zn slightly reduced the tensile strength of PLA from 64.9 MPa of the control PLA to 60.1 MPa, which met the requirements of most practical applications.