Highly dispersed red phosphorus produced by mechanical milling for enhanced flame retardancy of polyurethane-based foam

•The high-energy ball milling is adopted to prepare red phosphorus/diatomite flame retardant.•Diatomite with high specific surface area exhibits synergistic dispersion with red phosphorus.•A low exotherm polyurethne/watergalss foam with excellent flame-retardant effect are prepared by free-foaming method.