The Influence of Transition Metal Oxides on Flame Retardant and Smoke Suppression Properties of Rigid Polyurethane Foams

In this work, expandable graphite (EG) and ammonium polyphosphate (APP) were used as flame retardants, and transition metal oxides (Cu₂O, Fe₂O₃, Ni₂O₃, Co₂O₃) were used as synergists. The flame retardants and synergists were applied to prepare for flame-retardant rigid polyurethane foams (RPUF) at the same total contents of 30 php and the same mass ratio among APP, EG and transition metal oxides (15: 13: 2). Then, tests of limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimeter were used to investigate the flame retardancy and smoke suppression properties of RPUF. The experiment results of LOI and UL-94 showed that the flame retardancy of RPUF/APP/EG was improved more or less by addition of transition metal oxides, in which only the addition of Cu₂O could improve the LOI value to 25.5%, exhibiting better synergistic effect with EG and APP than Fe₂O₃, Ni₂O₃ and Co₂O₃. Besides, the addition of Cu₂O could further decrease the total heat release and total smoke production of RPUF/APP/EG by 22% and 20%, respectively.