Fire retardancy of a reactively extruded intumescent flame retardant polyethylene system enhanced by metal chelates

A reactive extrusion technology was adopted to synthesize a flame retardant (ER), based on the esterification of melamine phosphate and pentaerythritol. The ER imparts good flame retardancy and non-dripping for polyethylene (PE) when combined with ammonium polyphosphate to yield an intumescent polyethylene (PE-IFR). The performance of this intumescent system has been enhanced by the addition of small amounts (0.2%) chelated copper(II)salicylaldehyde (CuSA) and salicylaldoxime, (CuSAO). The thermal stabilization and burning behaviour of the flame retardant PE system have been investigated by TGA, LOI, the UL-94 test and cone calorimetry. All formulations studied provide good flame retardant behaviour, with LOI ≥ 27.4 and UL-94 V-0 rating. The onset of decomposition in TGA for flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) commences at lower temperature than that of PE with release of blowing agent, but continues to a higher temperature, leaving a greater residue. Significant differences have been observed in burning behaviour using cone calorimetry, between flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) and PE, showing decreases in HRR, PHRR, MLR, FIGRA and CO emission.