The synergistic flame-retardant behaviors of soybean oil phosphate-based polyols and modified ammonium polyphosphate in polyurethane foam

Vegetable oils, as raw materials for polyurethane foam, have attracted much attention for being non-toxic, biodegradable, renewable, and so on. However, polyurethane foam burns extremely easily and the vegetable oil grafted phosphorus/silicon flame retardant polyols alone do have insufficient fire-retardant efficiency. Herein, a new bio-based flame retardant (Polyol-P) was successfully synthesized through a ring-opening reaction by using epoxy soybean oil and phenylphosphonic acid as raw materials. Then, Polyol-P was first combined with melamine-formaldehyde resin-microencapsulated ammonium polyphosphate (MAPP) to modify polyurethane foam. The synergistic flame-retardant effects of Polyol-P with MAPP in polyurethane foam have been studied by thermogravimetric analysis, limiting oxygen index test, vertical burning test, and cone calorimeter. TG test results showed the addition of Polyol-P and MAPP promoted the degradation of polyurethane foam composites and the char residue rate at 800 °C of PU-P/15MAPP was significantly enhanced. Flame retardant test results confirmed PU-P/15MAPP exhibited LOI of 25.8% and passed the V-0 rating in the UL-94 test. Cone calorimeter test results indicated the peak heat release rate of PU-P and PU-P/15MAPP reduced from 395.10 kW/m2 to 291.92 kW/m2 and 222.72 kW/m2 compared with PU-0. Furthermore, the ratio of CO and CO2 remarkably reduced and the residual carbon yield of PU-P/15MAPP was the highest, and its value was 20.0 wt%. SEM confirmed that the char residue of PU-P/15MAPP was wrinkled and uneven, which was caused by the release of many volatile gases. FT-IR verified the formed structure of the phosphorous-containing carbonaceous structure. These results suggest that Polyol-P and MAPP have a good synergistic flame retardancy on polyurethane composites and can reduce fire risk.