Synthesis of a novel polyphosphate and its application with APP in flame retardant PLA

To improve the flame resistance of PLA, a novel phosphorus-containing flame retardant (PFRS) was synthesized via the A(2) + B-3 type reaction of bisphenolic acid-based monomer (DPM, A(2)) and phosphorus oxychloride (POCl3, B-3). Flame retardant PLA composite containing 15 wt% PFRS could achieve an LOI value of 24.3%, as well as a UL-94 V2 rating. Based on the structure of PFRS, here, intumescent flame retardant (IFR) systems were prepared by combining PFRS with ammonium polyphosphate (APP). The resultant PLA/PFRS/APP samples showed excellent fire-resistance properties such as self-extinguishing behavior and extremely low heat release rates. The LOI value of PLA composite with the addition of 3.8 wt% PFRS and 11.2 wt% APP could reach 29.7% and pass UL-94 V0 rating, and the PHRR value decreased by 46% compared to pure PLA. Investigation of the morphologies of the charred residues by Scanning Electron Microscopy (SEM) and Raman spectroscopy revealed the intrinsic charring ability of IFR systems to form a heat-protective intumescent-like barrier on the surface of PLA.