Rigid polyurethane foam composites based on bivalent metal phytate: thermal stability, flame retardancy, and fire toxicity

As the main form of phosphorus in plant seeds, phytic acid has potential value in flame retardant field. In this study, a series of bivalent metal phytate (PA-M) flame retardants were prepared using phytic acid and divalent metal salts as raw materials. FTIR, SEM-EDS, XRD, and TG tests confirmed that copper phytate (PA-Cu), zinc phytate (PA-Zn), cobalt phytate (PA-Co) and nickel phytate (PA-Ni) were successfully synthesized. Furthermore, flame retardant rigid polyurethane foam (RPUF/PA-M) composites were prepared by one-step water-blown technology using PA-M as flame retardant. TG test results showed that RPUF/PA-Cu30 had the highest char residue at 700 C, which was 26.2 wt%, significantly higher than 12.4 wt% of RPUF. Cone calorimetry, smoke density test, and TG-FTIR analysis confirmed that RPUF/PA-Co30 composite exhibited excellent smoke suppression and toxicity reduction performance when 30 phr PA-Co was added. Compared with RPUF, the THR, TSR, and SDR of RPUF/PA-Co30 were decreased by 13.9%, 27.3% and 43.9%, respectively, and the release of toxic gases (isocyanate compounds, aromatic compounds, CO and HCN) and combustible gases (hydrocarbons and esters) were significantly reduced. The analysis of char residues of RPUF/PA-M composites suggested that PA-M could promote the formation of dense carbon layer with high graphitization degree and improved the fire resistance of composites. This work provided a new way for fabricating fire safety RPUF composites.