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In this work, the investigation mainly focused on the synergistic effect of phosphorus-containing polyol (BHPP) and nitrogen-containing polyol (MADP) in improving the flame retardancy of EG/rigid polyurethane foam (RPUF). BHPP and MADP were synthesized through dehydrochlorination and Mannich reaction, respectively. The influence of the weight ratio of BHPP and MADP was studied by thermogravimetric analysis and limiting oxygen index (LOI) tests. The results demonstrated that the optimal weight percentage of BHPP and MADP in flame-retarding RPUF was 1/1. In addition, the incorporation of expandable graphite (EG) into the RPUF/BHPP/MADP system could greatly improve the flame-retardant properties of RPUF composites. When the content of EG was 15 wt %, LOI value of RPUF composites reached 33.5%. Furthermore, the value of the peak of the heat release rate was reduced by 52.4% compared to that of pristine RPUF. Based on the analysis and discussion, a condensed flame-retardant mechanism was primarily proposed.

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