Synergistic effect of metal oxides on intumescent flame-retardant PP systems

Three metal Oxides, Bi₂O₃, Sb₂ O ₃ and SnO₂, in different amounts were added into the polypropylene (PP)/ammonium polyphosphate (APP)/and di-pentaerythritol (DPER) to study their enhancing effects on the intumescent flame retardance (IFR) .The flame retardance of the PP/IFR composites was tested by the oxygen index (OI). TG, TG-FTIR and SEM were used to study the decomposition processes of PP/APP/DPER, APP/DPER and single APP or DPER with Bi₂O₃. The results showed that Bi₂ O₃, Sb₂O ₃ and SnO₂ could increase the OI of PP/APP/ DPER, and maximum OI values were found with increasing the amounts of the metal oxides. TG showed that Bi₂ O₃ inhibited degradation of the APP/DPER at high temperatures and increased the charring; TG-FTIR indicated that the existence of Bi₂ O₃ changed the release of NH₃ and phosphorous oxides in the degradation process. SEM showed that the 0.1 wt% Bi₂O₃ made the char of the PP/APP/DPER homogeneous. Adding 0.1 wt% Bi₂O₃ and 1 wt% nanoclay into the IFR PP,the value of OI could reach 28.3% with 20 wt% retardant; the UL-94 could reach V-0 with 25 wt % retardant. The mechanical properties of the IFR PP system also increased by adding retardant with 0.1 wt% Bi₂O₃ and 1 wt% nanoclay.