Flame retardant, mechanical and thermal insulating properties of rigid polyurethane foam modified by nano zirconium amino-tris-(methylenephosphonate) and expandable graphite

A novel phosphorus-nitrogen flame retardant, nano zirconium amino-tris-(methylenephosphonate) (Zr-AMP), successfully synthesized by allowing amino trimethylene phosphonic acid (AMP) to react with ZrOCl center dot 8H(2)O, was incorporated into rigid polyurethane (RPU) foam with expandable graphite (EG) to prepare flame retarded composites. A synergistic effect between nano Zr-AMP and EG on flame retarded and physical-mechanical properties of RPU foam was observed. The RPU foam containing 3 wt% nano Zr-AMP and 12 wt% EG (RPU/12EG/3Zr-AMP) achieved a UL-94 V0 rating with a limiting oxygen index of 30.5%. RPU/12EG/3Zr-AMP showed a 74.4% reduction of peak heat release rate relative to untreated RPU foam. Furthermore, RPU/12EG/3Zr-AMP possessed lower thermal conductivity compared with the RPU foam with 15 wt% EG (RPU/15EG), while the compressive strength of RPU/12EG/3Zr-AMP was enhanced by 40% compared with the one of the latter. The thermogravimetric analysis showed that the simultaneous addition of nano Zr-AMP and EG had a positive impact on improving the char yield and thermal stability of RPU foam. (C) 2019 Elsevier Ltd. All rights reserved.